When DONT you use repair & first aid in battle?

pizzastorm: A repair kit is a must for most tanks. When and if you use it depends on the situation. I would suggest never repairing an orange track. There are so many other things that are useful to repair. The main ones being ammo rack, damaged gun, engine, or if you are tracked in a spot where you are going to lose a lot of your life.
I try not to use my repair kit on my tracks unless I am being hammered by multiple tanks or being perma tracked in the same spot. Being tracked occurs so often that I only try to use it if I feel like I will be rendered useless if I do not.
I use the Auto fire extinguisher on most of my tanks for a few reasons. The first being I do not get set on fire that often so it does not eat into my credits. The second being it lowers the chance you will get set on fire at all. And last of all, I often panic and it takes me forever to put the fire out manually.
Hope this helps.