Chad Callihan is not the biggest fan of in-place upgrades:
How many SQL Server upgrades have you been a part of? Was there much discussion about whether or not to do an in-place upgrade versus a side-by-side upgrade? I’ve been part of both and to me there is only one safe way to perform upgrades. Let’s go over some pros and cons of each and see if you come to the same conclusion.
I did kind of spoil the answer, but click through to understand why one is so much riskier than the other.