Code-only purists are still prominent in the iOS community. Yeah, there’s definitely baggage one must take on when using IB but the ease of being able to instantly preview your layout in different sizes is the big seller for me.
For smaller apps, with a team of 2-3 people, IB is fine....
The constraints are impossible to code review in XML since they refer to elements by IB ID which is essentially obfuscated. I don't understand why IB doesn't let you give the elements their own human-readable IDs.