I use 0.8mm solder for quite a lot of things (I do repair older electronics) and 0.46mm for newer projects - that's only for thru-hole. For surface-mount it's always paste from a syringe.
Personally, I don't think I could work with anything thinner than 0.46mm - but it really is a preference and 'preferred technique' sort of thing.
I've seen guys using really thin solder and they seem to do a 'heat it up and feeeeed it in', whereas I think I'm a 'heat it up and dab some on' kinda guy. Has sort-of-parallels to MIG vs. TIG if you've done some welding.
Yours,
TonyWilk