Yes I do sometimes. I don't do every one but I do straighten seams by going over them again when I think the seam is crooked or I have dipped in a place or two.
It is stronger and can be worth doing but I don't generally do it for that reason. I do on somethings that will get a lot of wear and tear tho.
I think it is a good prevention technique if you know the item will get dragged around alot. I don't do big quits tho