I'll stick with pinning the seam line horizontally with fine pins making sure that only the tip of the pin is lined up with the seam just for the rare instance when I don't pull it out in time. Besides, it's far less annoying to pull pins out as I sew than to carefully unpile several feet of sewn fabric and retrieve a mess of pins before I can press what I just stitched.

I set a pin at the very end of the seam line and pull it out slowly at a slight upward angle to keep that last little bit of fabric from pulling to the left. Works every time. Enders work, too, but they're an extra step and extra thread.

I recently decided to switch to those fine extra long daisy or butterfly flat head pins, which are much more convenient to remove and work with-I try not to sew over the pins, however, I noticed I am CONSTANTLY getting stuck by them. I use them for making my purses, so I have to pin allot-I guess I am just not used to the length. I have to keep a tissue next to my machine to blot the blood! (sorry if that's too graphic!).

I pin vertically too and about an inch from the edge so I can just keep sewing.
Works really well specially if your fabric is well starched. If I'm matching seams
I stick a pin where the seam should meet and then put another pin vertically
and remove that first pin.

I pin Horizonal to the seam on the sewing line and remove pins before sewing over them. Also I was taught when matching seems do not pin directly on the seam but on either side since pinning on the seam will not make seam match but rather make it shift .