Are there phase issues when tracking acoustic direct in and mic at same time?

Folks-

Do you do this? Under what circumstances? Interested in what folks do with this tool- it was not available in the 'old days' when we simply observed good 3:1 ratio and other guidelines. Does delaying spot mics assist you in getting better audio now that this tool is available? Your thoughts?

I was reading on the net,
somebody suggested time aligning room mics.

I had never done that before, as I always wanted the room sound.

So I tried it, basically yes you do get more low end, but it sounds like the mic is in front of the kit, almost like you shrunk your room.

My question is when and why would you do this?