Close Account Option - How dangerous is that

Close Account Option - How dangerous is that

Hi

We noticed that there is an option for every user to close the account. This is accessible from the Profile dropdown >>Home and also the Settings tab.

Even non admin users have that option. 

What does this do, if for example we have a disgruntled user and such suer selects this option? What data is deleted?
And logically, is there a way to disable this option?

Thanks
Tom