[GRASSLIST:17] Why use a database?

[Michael Rensing]

I see that the dbf database is the default for adding attributes to 
vector layers, but I'm not sure what else you need a database for in 
GIS. I thought I'd ask the enthusiasts.
- Why would I want to use (e.g.) SQLite instead of dbf?
- Why would I want to use PostGIS?

Would any of these solutions speed up the loading and/or processing of 
layers, either raster or vector, or both?

TIA,
Michael