TEC, can anyone use small words and explain this to me?

OK, one thing I've never really understood is the point
of Tower Enroute Control. Maybe it doesn't apply much
here in the Midwest where there's space between TRACONs.

Can anyone explain this to me, using small words and speaking
slowly?

Specifically, when is this used, what is the benefit, how
does one find out whether it's an appropriate thing to request,
and how does one request it? For example, I know there are
listings in the AF/Ds for TEC routes, is TEC only available
on these routes? What is the benefit of TEC vs. other routing?
Is TEC available on any route where one is controlled by TRACONs
all the way? What about a route where one passes directly from
a DP to a STAR with no enroute section in between?

TIA for any assistance.

Very confused on this subject Sydney