Almost correct! Actually, the reason we call it a "unique" IP rather than a "static" IP is that it can change (and on occasion, it will!).
In addition to the things Scott mentioned that it is needed for, it has an additional characteristic in that it is not shared (it is unique to your site), and this can be of interest to those worried about work/school site blocks, as you can't pick your neighbors on a shared IP address.
--DreamHost Tech Support