I thought that I had above?
2.5" drives are more portable/compact and normally powered directly from the USB port(s) without the need for an external power supply. Small box that you just plug in and that's it.
3.5" drives are more bulky and always require an external power supply unit and maybe also fan cooling etc. so you have more bulk/weight and annoying cables.
The former are good for carrying with you on the go. The latter are good for fixed installations or maybe intermittent portability but not carrying with you day to day. 3.5" drives also come in much higher capacities than 2.5" drives but the latter are getting bigger these days.
2.5" drives are more portable/compact and normally powered directly from the USB port(s) without the need for an external power supply. Small box that you just plug in and that's it.
3.5" drives are more bulky and always require an external power supply unit and maybe also fan cooling etc. so you have more bulk/weight and annoying cables.
The former are good for carrying with you on the go. The latter are good for fixed installations or maybe intermittent portability but not carrying with you day to day. 3.5" drives also come in much higher capacities than 2.5" drives but the latter are getting bigger these days.