Amazing.
I do it about every 2 years or so. Whenever I "feel" things are clogged up. Most likely unnecessary.
I did do an in-place upgrade with an ISO many times because windows update keep having errors and not completing the upgrade. But it still carries over all the old apps and settings. I have a lot of registry macros that load in all my custom settings quickly. I think if you have a local account only, in-place upgrades don't ask you to make an online account.