Receiver setting for subwoofer?

Question

Is there any reason I shouldnt run the "both" option, ie bass coming from the sub and my front/floor speakers? The subwoofer seems to operate at the same level/efficiency whether the receiver is set to just the sub option or if i set it to both, where I'm unsurprisingly getting a bit more bass. Thoughts?

The speakers and sub are both polk

Answer 1

 i just perchased a jbl subwoofer and i need to know about the two switchs on the back one switch says phase and it has the #0 to180 and the other switch says LFE and normal can you help me. 

Answer 2

 i just perchased a jbl subwoofer and i need to know about the two switchs on the back one switch says phase and it has the #0 to180 and the other switch says LFE and normal can you help me.