Depends so much on so many things. Like, what kind of app/company are you building? How big is the company/app/team(s)? Who is on your team? What are your other practices? Etc..
For example, if my team was very junior, I'd be less inclined to merge first, but if it was very senior, I'd be more inclined. But even then, it depends on other factors.
For example, if my team was very junior, I'd be less inclined to merge first, but if it was very senior, I'd be more inclined. But even then, it depends on other factors.