If you're a small company, just starting out, and you're not locked into Photoshop for some reason, there's no reason to start producing files in that format. I
But when you want to hire employees or freelancers or accept files from clients or send files to a printer or basically do anything beyond doodling in your bedroom you are locked into the Photoshop/Indesign/Illustrator/PDF/EPS Adobe ecosystem because it's the defacto standard in the creative market.
Which is a main point of TFA.
No man is an island if he's on at least one mailing list.