I don't think one view is inherently better than the other. Some people prefer unified, some people prefer side-by-side. If you want a bigger audience for your product, you may want to offer both options. I was looking for the option and ended up here.

One thing that is made slightly easier by unified view, is staging changes line by line. With unified, I can select the last lines of a block of deleted lines and the first lines of an adjacent block of added lines and stage them together.

Line-by-line staging was one of the reasons I used SourceTree and the reason why I use SmartGit after switching from macOS to Linux.