Just recently learned about parallel compression as a mixing technique. I was watching a video with Steve Duda saying he likes to  mix in a very heavily compressed version of the mix with a non-compressed version. Out of curiosity wouldn't mixing in the compressed signal produce lots of phase problems from the two mixes sounding the same? Or is that not an issue at all? 

I use parallel compression lots of times in Reaper, never had phase issues.

There are also a lot of compressors with a dry/wet knob. And with FL studio, you can mix each effect in the mixer track with the dry sound, so you can parallel process any vst effect you like. I guess almost every DAW can do this.

yea you can make things really thick, but it's easy to over do it.