Why should I use a dependencies manager?

[CBy]

Hi,

I like to setup my projects in such a way that new users can check them 
out from our subversion repository and are ready to go. For managing 
dependencies, I have been experimenting with both Maven Ant Tasks and 
Ivy. Now that I have to choose between them, I seem to have forgotten 
why I started this exercise in the first place. Granted, checking in 
log4j and other libraries that I use in almost every project is not very 
efficient, but who cares? It's simple, has none of the bootstrapping 
problems, and disk space is not really a concern nowadays. I like 
simple. Is there a compelling reason not to do it this way? (I've read 
the FAQ, but was not really convinced so far.)

CBy