I've found that I'm using this feature much more than I thought I would in arc. Before, I'd figure that it's the same as opening two windows side by side. It's not, having it as a built in feature opens up a lot of things. Opening an article on HN and the comments on HN side by side, for example. I NEVER did that before, now it's second nature.

I was trying out Arc and almost forgot about it, but now knowing about this feature changes everything, thanks for pointing it out! Very often I need to see two or more pages side by side and I just hate making a mess in my browser with multiple windows open. They just tend to get lost and I have to move them out of the way or close them one by one, it is just annoying.

You can even have more than two splits, which I did not expect. Also, holding the option/alt key when clicking on a link opens it in a new split which is super convenient.

Zen browser does this as well though as a Firefox derivative, though as a quick disclaimer it is a relatively new project.

https://www.zen-browser.app/

Vivaldi has this functionality as well, although the UI around it isn't great. There's no easy way to swap one pane with a different site - you have to untile the existing sites and retile the ones you want.