In FTL, you can place crew members in various subsystems to gain bonuses. However, I don't know how to actually quantify those bonuses. The two that are least clear to me are:

* Manning shields increases shield recharge speed.
* Manning weapons increases weapon recharge speed.

While I understand the general effect, I'm not sure how much of an actual increase I'm actually getting from these. 

Also, in FTL: Advanced Edition, it looks like you can man the sensors and doors.

Finally, does manning it with multiple crew members give a larger bonus?