I could not disagree with Tom more! I find a densitometer invaluable, specially if you are just beguining. Testes for correct film speed, testeting for correct developing can tell you if you are doing things right or not. In other words finding mistakes is a lot easier than if you say, well let me half the EI, or let me double it and lets see what happens if I do an 8 min developing.
All this is fine if you are an experienced photgrapher and have some ideas based on that exprerience, but if you have no experience this type of working method will lead to frustration and many, many wasted sheet os film.
Of course also depends on what you do, I print in pt and could not live without one, t saves me a lot of money, but if you are a commercial photographer, doing work with digital backs, you definitly do not need one.....