it is up to you= you get different answers because different people do it differently. some stitch right on the seam or as close as they possibly can- others stitch 1/8" from the seam...and some 1/4" but still consider it sid...
if you run right along beside the seam it will reinforce it's strength. sometimes the decision is made by how difficult it is to stitch do what works for you and gives you the look you like...there is no right or wrong-just different opinions