I pin long seams together - in fact I halve and quarter them before joining them - and then match the half and quarter points. I do measure them first to see if they are the same length.
If there are a lot of intersections that are not behaving well, I pin them. If they are behaving very badly, I baste them first before sewing them with small stitches.
Piecing small pieces together, generally I just hold them together.