That's a very good point. Definitely disable for randoms finding your lobby/game though. At least this way, even if someone (presumably a friend) clicks "join session", you know they shouldn't suck (or too much lol).
But yeah, yesterday we had our Team Booster guy disconnect. He had upgraded it to max straight away in the first area, which I really liked about him doing, because it makes a huge difference for us Engineer's and Medics.
The weird thing though, I think he was a Weapons Specialist.
I never use that class and definitely not with team boosters, but if you upgraded weapons specialist to have faster reload, if you then used team booster, would your reload be even faster?