I recently re-installed Ubuntu on my desktop computer. It was about 8 years since the previous full install. I'd kept it up to date with latest Ubuntu upgrades. I wanted to change the hard drive configuration and put most of the os on a solid state drive. There was also a lot of cruft that I had installed over the years and a clean slate would get rid of tons of software I no longer use.
The re-install worked very well. The most noticeable improvement was boot time. Partly from the solid state drive and partly from the removal of all the extra software. I didn't lose much in the process. I have a script that installs software that I use that isn't included by default. The script also tweaks a bunch of settings. But, the one thing that I lost was my global key bindings.