It should be offered as an option really.

One caveat is that you need to think ahead about how much space you want to assign to each partition. You could end up with your /home/ partition being full while the system partition still has plenty. Or vice versa. You can manually readjust the boundaries but it requires some understanding and can’t be done on the fly by a non-technical user. By contrast if everything’s stored on the same partition you never have to worry about this.

You can, by the way, manually recreate this set up even after the initial set up although it will require lots of free space to shuffle around files (or some external storage to temporarily hold them). Basically what you do is create a new empty partition, copy all your /home/stuff there and then configure your system to always mount that partition as the /home/ directory when it boots. Files are just files after all and the operating system doesn’t really care where they come from as long as the content is correct. Once you got it working you can delete the originals and free up the space to be used otherwise.

Typically your personal files and app settings are stored somewhere in your user home folder, eg under /home/bob/. Ideally you’ve set up your system in a way so that the entire /home/ folder is stored on its own disk or partition at least. That let’s you boot up a different distro while using the same home directory. But even if you haven’t set it up separately from the rest of the system, you can still manually copy all those files.

Not every single application setting is transferable between distros as they sometimes use different versions but generally it works well. Many apps also let you manually export profiles or settings and reimport them elsewhere later. Or they have online synchronization baked in.