I live in France and these things are in every McDonalds already. I did not realize that they were not common elsewhere.
Ordering at a self-service kiosk is convenient because few people uses them, so usually there's no queue. This may be related to the fact that they only take cards. Ordering from the kiosk also prevent misunderstandings.
I've also used their mobile app and their website to order (for pick-up, they don't do delivery) but the benefits are minimal compared to ordering from the kiosk. Paying with a card on a mobile phone is annoying, especially when 3D-Secure kicks in and I have to copy the confirmation number from the SMS to the app. I'm sure that for McDonalds the main benefit of the mobile and online offerings is that they lock in the customer and prevents her/him from changing their mind on the way to the restaurant (but not really as you pay only if you collect the meal).