Not sure what you mean.
I do not cross my sub at 80, my speakers are all set to 80 and small, which means they play everything down to 80hz, and the rest is directed to the sub + the LFE content (keeps sub from being localized). The LFE channel is completely different. It can have content up to 120hz that is meant for the sub only, and should, so the rule is to keep your LFE channel at 120hz so you arent clipping anything meant for the sub.
If you set the LFE channel at 80hz, anything above that meant for the sub goes, well, no where. It is lost IIRC. Granted, this is a small issue in content, but the speaker crossover and LFE crossover are two different things and functions.
Now setting your fronts to something higher than 80 when they can play that low is definitely a bad move, because you are sending content to the sub that it does not need and it can be very localized. I used to have small fronts that had to be set at 100hz, it was kinda annoying.
I never know where my subs are, but I sure know they are doing something.
65" VT50 / Oppo 103D
Denon 4520CI / Emotiva XPA-3
Klipsch RF82 II and RC62 II / Hsu VTF-15H (2)