Any scenario where you'd want to use the speaker phone has little to do with noise. Sometimes I want it while driving because I don't have a headset (and don't plan on getting one, since I don't own a car and drive rarely). Or in the shop while drilling, soldering, or whatever. Or outside working on something. It's about using the phone while doing something else, often something that you couldn't do with something blocking one ear or dangling anything from your head. Then of course there's the case where multiple people are listening/speaking through the same phone.