I really like seaming pieces that have had the first stitch of each row slipped - I find it much easier to see which stitches are to be used for seaming and it still produces a really nice, finished edge.
One thing I did once, though, that I'll never do again - it was on a baby sweater that had set in sleeves. On the body section of the sweater, I slipped the first stitch of each row up the sides and then continued to do so when shaping the armhole. This was not a good idea!!! Because the top of the sleeve that got seamed to the armhole was a bound off edge, it was VERY difficult to match up which of those slipped stitches went with which sleeve stitches for seaming.
So, I'd say if it is an edge that is going to be seamed to an equal edge (for example, the side seams of a sweater), slipping the first stitch is a great way to go.