Should I use GHC Haskell extensions or not?

Question

As I am learning Haskell, I see that there is a lot of language extensions used in real life code. As a beginner, should I learn to use them, or should I avoid them at all cost?

Answer 1

The other answers here are good ones. I would add that GHC extensions are not as future-vulnerable (*) as they might be, because GHC seems to be far and away the most popular Haskell compiler, and I don't see that changing soon.

(*) as in the opposite of "future-proof"