1) It's faster for self checkout because the line moves faster (one line for multiple checkout stations) and because I can scan my items faster than they can. However, Aldi checkout lines move ridiculously fast, so this ends up not mattering much.

2) I get to pack my own stuff, most cashier employees don't pack things to my liking (eg cold items should all go in the same bag so they help keep each other cold, but they don't always do this). At Aldi, you pack your own bags anyway, so this is not an issue.

3) Talkative cashiers. I don't care to talk to a random person I'm never going to see again, but at Aldi you don't have to because you'll be so busy trying to load your items on the conveyor belt trying to keep up with the cashier that they won't have time to talk to you (see #1, and no I'm not joking, it can be hard to load up the belt fast enough to keep up with them if you don't have a significant head start).