Freemium games (free to download, free to play, but with premium offerings) account for a significant chunk of the tens of billions of dollars generated every year through in-app purchases. Gamers feel much better about spending money in a game they're already enjoying than on a game only due to a beautiful box or homepage.
If the objective in a game is, for example, to reach a higher level, gamers should get any boosters back that they used in vain. It's unfair to pressure gamers to throw good money after bad in the sense of having to buy even more boosters because the first one(s) clearly didn't help and would otherwise be lost.
The rules for a booster refund must be workable. A refund can only be granted when it's beyond doubt that one or more boosters were used in vain. In level-based games, that determination is easy: you advance or you don't. If the objective is to collect points, the case for a refund is clear where you get zero points despite using boosters.
A booster gives players more strength, provides valuable information, or reduces/removes an obstacle. Extra moves/time aren't boosters in this regard: they're like renting a tennis court for another hour. What's key is that you can decline to buy more moves/time because you'll get your boosters back in case you don't make progress.
In a scenario that qualifies for a refund, it's up to the game whether you get your boosters back (so you can use them again) or whether the refund is made in the game's in-app currency. As long as you don't have to write your failed boosters off as a "sunk cost", you get the benefit that matters.