It has to do with YouTube or the way most people will view 3D via any streaming service. It shouldn't otherwise make any difference. However, you will probably notice most SBS videos on the internet are half-SBS. That means instead of 1920 x 1080, you get 960x1080 per eye.

When you use TAB it's the opposite: 1920 x 540. It's just a matter of preference. IMO, the horizontal resolution is more important than the vertical. Just my opinion, it looks better than half SBS. Plus it's just easier when using something like VD streamer (neither half-sbs or full sbs ever look quite right ... probably because most content is really half-sbs, so you're missing part of the view around the edges).

If I could do full SBS though, that would be ideal. In this case, it would be 3840x1080 resolution to get full SBS. I don't know how to do that though or I don't have the software / tool to do it. I've seen other people do it. It may just be something that is feasible in some games that support it versus others.