Data backup needed before Apple Store screen repair?
You need to backup your data.
Period.

There is a new adage for the digital world we live in...


  "Any data which is not stored in at least three distinct locations ought to be considered temporary"


This translates to one on-site backup, e.g. Time Machine -  &amp; one off-site backup, iCloud, BackBlaze, CrashPlan etc.

The first is to cover for if you break your machine irreparably.
The second is for if the house burns down too.

Without both your data can be lost at the 'whim of the gods'... forever.

Please have a read of my somewhat tongue-in-cheek question I posted on the Ask Different Meta a while ago

Restore from backup?