connecting subwoofer via speaker terminals

why would you go from the speaker to the sub and not from the amp speaker out?

@parkergetdean Why have a long run of wire from the amp out to the subwoofer? The sub is near my main speaker and is a short jump from the speaker over to the sub. Much less wire. The sub input requires very little signal from the speaker terminal and doesn't need any special wire. 

@gdaddy1 understood, thanks!

@fastfreight  +1

My speakers have good bass to about 45hz so let them do their job. The subs low pass is set at 60hz.  I tried using high pass filters but, like you, I much prefer the full signal going to the mains. I also agree the imaging to be better/cleaner as well. Keep it simple!

So much better ultra deep bass when using the low level inputs to the subs rather then the high level.