You can erase your friend's save file with PS4's Share Play

[SvennoJ]

Burek said:

Oooh, I wonder if it allows friends to make in-app purchases!?!

You know, wonder into the menus, select downloadable content, and purchase a horse armor or a few dozen Ultimate Team packs...

If you give them your password, sure they can. They won't even need share play :p
I doubt it would work with share play as those in app purchases usually launch the store which is locked out I think?