Help Jelly Bean update worth it?

I finally got an update notification for my Xperia P which Sony says is for the upgrade from Android 4.0 to 4.1.

A friend had a similar option to upgrade her Galaxy Note from 4 to 4.1 and went back to 4. She said that the upgrade went through too much storage space and wasn't worth it for her.

I'm not sure how much she knows about phones, can anyone who made the upgrade advise if it will impact badly on storage space? I got rid of my HTC as they never seemed to put enough storage on the things.