This card is difficult to make use of, as a concrete loss of 6000 in LP advantage is rarely worth a +1 in card advantage. This is significantly different from a card that simply gives the opponent 6000 LP, or one that requires the user to pay or lose 6000 LP, as both of those downsides can be worked around (e.g. an "Exodia" Deck does not care about increasing the opponent's LP, and an FTK/OTK Deck does not care about paying a lot of LP if it will cause the player to win that turn anyway). However, this card actually requires the player to first put in the work to deplete 75% of the opponent's LP, before undoing that work in exchange for a +1. For example, this card will work badly in most "Exodia" Decks as they are unlikely to be able to deplete 75% of the opponent's LP in the first place, and it will also work badly in most FTK/OTK Decks as they usually aim to first set up the necessary combo pieces and then rely entirely on them to deplete the opponent's LP (making a card that helps the player draw into combo pieces after depleting most of the opponent's LP useless).
The use cases for this card can primarily be split between two situations, one where both players have low LP, and one where the player still has close to 8000 LP while the opponent has close to 2000 LP:
If both players have low LP
Use in a Deck with high offensive power that relies on momentum and card advantage rather than eventually beating down the opponent's LP (notable examples of such Decks include "Dark World" Decks and "Heroic" Decks). In a case where you have almost defeated your opponent but they have just taken momentum away from you (causing you to be nearly defeated as well), you may be stuck with no momentum (and thus no damage output) despite your opponent's LP being low, putting you at risk of losing thanks to your opponent's momentum. The +1 from this card may possibly provide a critical momentum swing big enough to give momentum and damage output back to you, giving you a chance to win from an otherwise lost position. Even this is situational however, as it is equally likely for you to have just taken momentum away from your opponent, in which case this card will provide no swing and will only increase the momentum that you already have, which is unlikely to be enough to quadruple your damage output (your opponent's 8000 LP after this card vs. 2000 before).
If you do pull off the above situation, follow up with "Hope for Escape" for another +~2 in card advantage.
You can attempt to maximize the momentum swing by using "Megamorph" or "Unstable Evolution", cards that are designed to turn a losing situation around.
Alternately, follow up with "Reversal Quiz" to possibly trade Life Points with your opponent.
If you have 8000 LP while the opponent has 2000 LP
In general, if you are in a scenario like this, you likely have either a lot of momentum over your opponent or enough time to gain said momentum, making the effect of this card near pointless. Most situational uses for this card involve the opponent intentionally lowering their own LP as part an OTK, allowing this card to counter it while simultaneously gaining card advantage (and wasting whatever card the opponent used to lower their LP).
If your opponent has intentionally made their LP low to use "Hope for Escape", activate this card to make them waste their card (along with whatever card they used to lower their LP). Your opponent is likely running an "Exodia" Deck, which will have little to no way of defending itself after running out of draw power, making their increase in LP inconsequential. (However, note that this counter will not work as well if your opponent is aiming to increase your LP rather than lower theirs to use "Hope for Escape".)
Counter an opponent's attempted OTK that uses some combination of "Megamorph" and/or "Unstable Evolution". If you have a little prior damage or have lowered your own LP slightly, this counter can also strand your opponent with some weak monsters at the end of their turn, giving you the jump on momentum.
The "Elemental HERO Air Neos" OTK revolves around the fact that if its controller has 2500 LP or lower, then a direct attack from "Air Neos" reduces the attack target's LP to 0 no matter how high their LP was beforehand. Use this card to stop said OTK and make your opponent have to spend the time to bring their own LP down to 2500 or lower again.
This card is unlikely to work well with cards that attempt to equalize a difference in LP. For example:
"Life Equalizer": In a best case scenario where you have 1000 LP while your opponent has 2000 LP and the Duel's momentum, you can activate "Heroic Gift" followed by "Upstart Goblin" followed by "Life Equalizer" to bring both player's LP to 3000. However, the result is a highly situational +0 in card advantage for you, making it unlikely to swing any of the Duel's momentum, and the relatively small change in LP this late in the Duel is not likely to have enough impact for this very risky setup to be worth it.
"Yu-Jo Friendship": If both players have 2000 LP, "Heroic Gift" followed by "Yu-Jo Friendship" alongside "Unity" can bring both players' LP to 5000. However, this cancels out the +1 in card advantage provided by this card, and again, a situational +0 in card advantage that provides no other advantages (in LP or otherwise) is unlikely to be worth it.
One use for this card can be to force a victory specifically with "Vennominaga the Deity of Poisonous Snakes", in environments such as some video games where the player can (or is required to) earn an achievement for winning with "Vennominaga's" victory condition and not by reducing the opponent's LP to 0. A major difficulty in pulling off a "Vennominaga" victory is that the battle damage inflicted by three of "Vennominaga's" attacks may well be enough to win the Duel on their own, which will void the achievement; this card can prevent this from happening.