Let's all keep in mind that this feature is meant as a means to help out your group-members.

Each Manager should take care of his/her own club and if they get in a tight spot, they can ask their group-mates to help out and spend a booster or two for their player (or several players). And they should expect that their group-mates will ask for the same at some point in time.

In general though, if I have to be completely honest, you should put your players up for loaning if you believe that you can help out your fellow FA mates and not just so you can get them to use all their booster reserves on your players.

Each rest pack restores 15% of a player's condition.
All five equal 75% condition.
This is a decent amount how ever you look at it (Be it spread out among 5 players or used on a single one), especially when you take in to account that you as a manager should be the one to balance your own resources and players so that you are at least decently prepared for a match. And may I recommend that if there is an issue with the condition of the club's players (I often find my self playing a match with around 75% condition), the manager should use the Condition bonus during a match.

The feature should definitely not be scraped if you ask me. It's yet another way to receive some help while managing your team.