Today you can use the local server and if cloud components are unavailable, then the some features don't work (but there are local ways to do them on HE)
Note 2 of the webcore forum describes what are cloud functions of webcore.
Primarily it is:
save restore pistons via cloud (piston sharing)
this can be done with local backup files of the piston
webcore's email service
HE has community apps for email or one can use notification services in HE
