It depends on the fabric and the cut of the pattern, how the finished seam would lay.
I really like french seams and do those when I can - I like that absolutely clean finish. I also like jean seams (I think these are also called flat-fell).
Sometimes I zig-zag the edges with no other finishing; other times, I press the edges before zig-zagging so the raw edge is more hidden (this depends on how much the fabric will fray, for me). Sometimes, I will do a modified french seam and tuck the raw edges in and zig-zag them shut; sometimes I will just zig-zag the two edges together and trim close to that.
I really can't say (other than how much fraying the fabric will do or how it will lie), what makes my decision (other than convenience too!) .... I'm an old 4-H sewer, so I do try to be consistent (i.e., no french seams when there will be a zipper set into one of the seams, since those won't "match" and it may not lay identically as a result of using a different finish on it than the other seams, etc.).
I very rarely pink - usually with polyester silkies and only with them.
But I also don't think I've ever *not* finished a seam in some way. I know lots of people just skip it, pattern instructions rarely talk about it - but I just can't skip it. I probably am not always doing purple or blue-ribbon sewing by 4-H standards, but I have to finish the seams anyway.
It's a compulsion I think.
I sew a lot, and I think that knowing "how" you want to finish seams on a particular garment is a learned thing - you're assessing
The weight of the fabric,
The way the pieces fit together (i.e., a french seam on a peasant blouse IME causes a "bunching" under the arm seam, so I use turned-over zig-zag finish on those when I make them for myself or Ina),
The amount of fraying you'd anticipate the fabric to do when washed,
How loosely woven the fabric is (may need reinforcing stitching)
The "drape" of the fabric (bulky finishing like a french seam may really impact the way a rayon fabric hangs in the end, for instance)
How much "wear" the garment will get (I try to finish well on kids' clothes because I expect them to be handed down and get rough use),