Guilds - not sure what's going on

Not sure I quite grasp what's going on with guilds.
- Heal kits, I don't use them. Got a strong squad which can be easily rotated, other than speeding up recovery from injuries what's the point?
- Guilds, I only have about 10 heal kits. If I join a guild do I need to buy more to donate to fellow team mates? Not interested in paying for them so wouldn't have many to donate to others.
Kits are free you and they dont come out of your pocket when you send them?
Kits are also useful to top up energy after , for example a draining tournament game or league game , to protect against immediate challenge from opposition when your energy is low. I have also totally swung a game by repairing a particularly good player and sending gem back into the same game following injury
Players train better with higher wnergy