I've multi booted OS's for years, namely a couple of Windows versions and Slackware or SuSE

Recently though I'd contemplated running two differing Linux distributions on same machine and a couple of things been bugging me.

Namely:

Can I use the same /home directory on both?
Now, obviously I can mount the same location and share it across two different distributions or even OS's but would two differing distributions happily share the same /home dir?

Yes in theory you can, but.....

- uid's / gid's must be the same for the user(s),
- different configuration files for the same programs could result in unexpected behaviour,
- possible package version problems.

I would advise against it.

If certain data needs to be accessible in both distro's I would create a separate partition and mount it (the uid/gid might still be an issue you should take care off).

Another approach to multiple distributions is to use virtual technology like KVM which offers a number of installations live on the computer simultaneously.

If you're going to go that route, I wouldn't clone /home between them. Or even /home/user/. But /home/user/mylargedata/ should share perfectly fine. That would avoid most of your large data duplication. While keeping your ~/.config files version happy. And perhap bypass the uid duplication that would be needed to share /home/. If you wanted to share some .config type files like your browsers cache you could always move it to the shared location and link to it. At the risk of versioning issues.

The main downside of dual booting is keeping each OS up to date on changes. I tend to run at least one machine on debian sid, and that by itself seems to imply 1GB of updates monthly for the girth of things I have installed. It's still less than 16GB for the total install, but annoying to update so much when you use so little at any one given time. But I need my office suite, media editor, development environment, and other trinkets.