I avoid putting them on the computer hard drive so that if something ever does go bad with that, I still have them on my thumb drive.
What do you guys do mostly?
A lot of people don't realise that Waves unique identifier is made up using info from various components in the computer.
Changing out the motherboard, for example, can leave you unable to access your licenses.
Lesson learned - If you're making any computer upgrades and aren't sure, move your licenses to the cloud first.
I had this happen a while back and looked into it. At the time I think I found that you could have one free 'fix it for me' per year but if it happened twice there was a lot of money involved.
Thankfully I was able to restore my computer's original configuration, move the licenses to cloud, then make my hardware changes again.
Pretty sure the rules are the same whether it's broken flash drive or broken computer. It doesn't matter if the computer gets formatted, or the flash drive gets formatted.
As long as Waves recognise it as the authorised device you can always 'put' your licenses back on it.
In the end I made the choice to stick with the on-computer solution.
I might lose a flash drive but I'll never lose my computer.
If you need to be mobile then flash drive (or laptop) is the way forward. Just make sure you don't lose it more than once per year.