I assume you don't mean joining rows and you're only talking about seaming.
Seaming in crochet is usually a whip stitch so it doesn't matter, you can use a needle if you want, although I prefer to use a hook.
Otherwise it depends.
If you're making a crocheted seam it would depend on the effect you want and what stitch the rows are.
If you want a bigger or smaller "rib" for a seam you could adjust the hook size but too much would cause puckering, which might be an effect you desire.
If you're only going into the top of rows like on a square the same size would keep you from having to increase or decrease to avoid puckering.
For non-squares, the height of HDC doesn't divide to the length of a stitch so adjusting hook size might be a good way to avoid puckering. But you can also adjust how many stitches per row you use, "2 on that row, 1 on the next" etc.