The idea behind launch tubes is to rapidly launch your small craft into combat. The explanations behind the idea have been, well, failures.
Ideally the launch tubes should provide a significant acceleration boost to small craft upon launch. That would make a basic assumption that they are in fact more catapult-like and use magnetic accelerators to provide a launch speed of say 10-14G's. The speed wouldn't technically degrade over time since there is no atmosphere, but some sort of idea would need to be applied to slow them down to their normal thrust-rated speed. Perhaps they lose 1G per turn until they reach their normal thrust. One minor issue would be getting the separate launch groups to the same speed as they formed into groups. Not difficult, but it does mean they would have to slow down to join up, thus giving thought to shedding speed.
Launch tubes also offer rapid deployment, something that hangars would be harder pressed to do under combat conditions. Assuming you have a packed hangar full of ships ready to be launched, they would be crawling with techs doing last minute servicing, arming them, fueling them, all the things that happen in real life. Which makes the packed hangars even more packed, which can slow down these processes. The launch tube would take fighters in their ready launch positions and drop them as rapidly as the tube can process them and get them launched.
Launch tubes should never be considered for recovery of fighters. That's just dumb, dumb, dumb. A damaged fighter, an injured pilot, anything at all could cause a wreck in the tube and take it out of service. A hangar bay is needed to recover craft (obviously it would not be able to recover as fast as a launch tube could launch).
One of the underlying problems with small craft is that the rules are for shit for them. They feel kind of tacked on because the idea was "it's space, we gotta have fighters!". And then when the rules were created they become kind of semi-useless. The rules for carriers are non-existent. There need to be rules for deck crews, re-arming, carrying external ordnance, etc, etc. Just like they are on real-world aircraft. So instead of the various publishers fixing the hole, it's been left to a mish-mash of players coming up with their own concepts and ideas (though crowdsourcing rules sometimes comes up with some pretty damn good ones!).
I say if you wanna discuss launch tubes don't use the book rules. The discussions will be far more productive and useful if you do so.