For me personally, it's just the convenience of always having my phone in my pocket. Sometimes when out and about and I have a bit of free time, but haven't brought my laptop, it's nice to be able to just pick up my phone and hack for a bit. I wouldn't do full blown project on it though.

I couple of years back, I really liked replit for having probably the best integrated IDE on a phone. Everything was so smooth and well thought out.