The writable is both very nice and very frustrating. The big issue is that it is a dumb bucket and it captures anything and everything you do or don't unless you exclude it.
Just to get a few things clear about the writable. When using a machine the writable always wins so if you for example install chrome 70 and the GI or appstack has Chrome 72 you will still get Chrome 70.
If you for example have Chrome installed in your GI or appstack and you decide to uninstall it from your machine with a writable attached your writable will create pointers in which it will delete Chrome. This means that CHrome is still in the GI or appsatcks but it is beaing masked as deleted by the writable. This can give you some very disturbing results if you don't know what is happening.
You also have the option to only use UEM for profile settings and use a UIA only writable (User Installed Applications). If you use this it wont capture any information in your profile.
Before using writable volumes for your users I would first fiddle around with it a bit to get an diea of how it works.
We are also using W10 with over 2000 writables and normally only need to reset 1 or 2 a week. If you capture profile information with UEM this would mean that user would get a new Windows installation because all settings are still there.