Synaptic: "removal" vs. "complete removal"
 

In Synaptic Package Manager, one can mark a program for "removal" or for "complete removal." When would I not want to "completely" remove it?

"complete removal" removes not only software in question but also configuration files for it. Use it when you are sure you won't be re-installing and wishing to keep the same configuration.

I use it on any old (Ubuntu) kernel to make sure all the modules get trashed as well.