I did a column on data base use in the June 1995 Chess Life. It is a fascinating subject, though, so here is another.
Many postal players prefer to think for themselves.
Many other players prefer to use previously played successful moves. In general, the stronger your opposition, the more likely you are to want to use a database. The database works like books on chess openings. What may be missing is the evaluation, giving instead the result of the game. This may be misleading with a limited number of games, but with a large number of examples a conclusion can be drawn about the evaluation of that opening.