Source based distributions enable the more experienced user to have a considerable degree of control over their system. Compiling and optimizing software for your particular hardware can bring noticeable performance improvements - however, compiling software can be a lengthy process. Another benefit of compiling a package instead of installing a pre-built binary is that some packages have optional parts in them with optional dependencies on other packages, which can be only selected at compile time. If you rely on pre-built packages, you can't make those selections any more. Usually the package maintainer chooses to switch all these options on, something which leads to the so called "dependency hell".
For more information on the various Source based distributions, click on the links below.