I've seen some websites that make their text unselectable. And I believe that this can break up user experience, as "selectable text" is a well established ui pattern on web and computer in general.
What is your opinion about disabling the functionality of selectable text? Is there any reason or example, proving that we should do that?
Edit: As was nicely mentioned in a comment, the above question seems to be targeted only for selectable text. But what I'd like to understand has mainly to do with cases where we should force text to be non selectable.