@valhalla When I worked at a clothing store, about 12 years ago, I was shocked to find the hems of some trousers to have been turned just once and then sewn down with the serged seam visible. Because that's just not how you make a neat finish, and I had studied to be a dressmaker.
But outside of that I've never thought that having serged seams would be bad, I love (and hate) my serger myself. 
Actually I find serged seams to be better than a french seam, cause the former is a lot easier to adjust for fit! (Which is not a thing in today's fast fashion with the nonexistent seam allowances, but at least you can take things in...)