Matter of taste - I really liked having two separate email apps, with different kinds of notifications etc. Just as I may dress differently for work, be in a different location, behave differently, I like my work environment to be different than my personal environment. So different email clients made sense to me. When I tried adding my exchange account to gmail, I found that they all mixed together, and I couldn't figure out how to view ONLY my work emails or ONLY my personal emails.
So I disentanged that (which isn't trivial, BTW) and downloaded the Outlook app.
Now I look at my calendar, where I DO want all my appointments in one place, because I'll risk missing something if I have to flip back and forth between two calendar apps. But it seems that I can't have that anymore. It was one of the great advantages of the Android calendar, that I could have my Google calendar and my Exchange calendar all in one place.
Google is actually punishing me for not wanting to use the Gmail app for everything! That's petty and bullying behavior.