With 7.4 it's not a big issue, with 11.1 obviously you don't want those contacts arcing like crazy (they're bad enough at 9.6v)
But the reason I push for a mosfet, is if your running LiPo, it's because you want to save space, or have more energy efficiency. Well what's the point of getting a 7.4v LiPo and running it at the same horrible efficiency of your stock wiring and trigger contacts?
This is why people think they need 11.1v LiPo batteries and realize all of a sudden their ROF is WAY too high and they don't know how to slow it down...
Well a 7.4v LiPo with mosfet and upgraded wiring will give you a really good ROF on most setups, typically equivalent to 9.6v sub-C NiMH battery.
Whereas the 11.1v will give you a higher rate of fire, while burning out your trigger contacts, then when you decide to get a 20$ mosfet to prevent your 35$ trigger from burning out again, and you might as well change all the wiring in there since you have to modify it all anyway, that's about $15 then all of a sudden your ROF goes through the roof and you break a 25$ piston
so $95, vs $35 to be on the safe side
Anyway good thing LiPo batteries are dirt cheap! Large batteries around $40, mini's around $12. And that's for good, name brand batteries, not that "comes from anywhere" airsoft brand stuff that WAY overpriced