I don't recall/haven't noticed Eminem doing it much in the past (I mean he might change his flow - but then he would stick with it rather than jumping back and forth). These days he changes his flow up all the time and it irritates the hell out of me. It's actually one of my biggest complaints with him these days (well aside from yelling and shytty content/pop anthems). He changes from rapping slow/normal to fast, normal voice/low volume to yelling, change back, changes again, etc - and he does it not only from one line to another, but within individual lines. I consider Rap God choppy for those same reasons.
It's just a personal preference thing I suppose.
Here's a perfect example :
In the first verse after the intro
he does a simple rhyme in the beginning.
Then switches to a complex scheme then
again goes back to a simpler flow to deliver
his punches.
He does something similar in the last minute.
He uses a really complex scheme then backs
off again.
All while changing his tone and tempo using both to
express several different emotional states.
Current Em seems to have abandoned all of that
and that's something I agree with.
This isn't to say doesn't still have schemes and punches
it's just that his style is really different now.