install and removing apps.... cleaning

[Richard]

when using synaptic to install apps, to try them out, then remove them,
is synaptic also removing the libs & other files, that the application 
needed at the time of install,
for the app, when using remove completely.

also, how can one check to see, if there are any libs (left overs) in 
the lib or bin,
folder (I think) that are NOT really needed by ANY application, OR the 
system,
other words, parts of application, that are sitting there and not being 
used by nothing.

is there a command to clean out left overs?

Thanks -
Rich