I do use stitch markers for counting my stitches, too. For example when casting on. In pattern setups I also use them to devide pattern repeats (every one or a multiple to them) to keep track more easily.
but in seed stitch I do never use that. It is so visible what stitch comes next. All it takes is a look at the pattern you have already made. I only can get off track when I don't look and think I know what I am doing. Mostly it works, but sometimes I have to knit back a bit.
but, yes, stitch markers are friends!