Hi there,
I'll start by saying I'm completely new to the pixel art scene (only been doing this for a little less than a month) so please forgive any misused lingo or dumb questions. Digital art is also something new to me and already I've had to do a lot of research in order to even get started. Fortunately, I've found a TON of great information on sites like this and Pixel Prospector- tutorials and old forum posts are incredibly helpful.
But no matter how much I search, I can't find any discussions on what I thought might be an important subject in top-down RPG's. And that's the choice between sprites that can move diagonally on the plane, and those who can only move up, down, left and right.
Here are some examples of what I mean-

In Pokemon you can only move up and down, left and right. So the Sprite has front, back and side views.

In Mother 3 you can move diagonally too, and so the sprites have left up/down and right up/down facing views (there's gotta be a better term for it) along with the rest.

And then there's games like Undertale, which have sprites with only four views but can still move diagonally.
The whole reason I bring this up, is because right now I'm currently in the process of creating my own character sprites, and I wanted to know which of these three forms of movement is more popular and why? I really like the sprites in the Mother series, and the idea of adding those extra frames for diagonal movement seem worth it, despite how much longer it may take to make all the sprites needed for a game. But is it practical or have any advantages? The aesthetic is nice, but how many pixel art games out there bother to use this form?
This is probably a lot of questions and maybe this is more of a game development question? I apologize again for any confusion. Any answers or thoughts on the subject would be appreciated. Thanks.