Cyberfly via AviationKB.com wrote:
The premise is
that it is not illegal to file an IFR plan and fly it VMC while keeping VFR
the entire time. It is very "ILLEGAL" to file IFR flight plan and fly in IMC
without either your IFR ticket or an IFR rated instructor.

One of the problems is actual clouds.

On an IFR plan, there are no cloud clearance requirements, and you can't
simply climb and descend at will to avoid them.

On an IFR plan, you are expected to go THROUGH even the occasional
cloud, which you can't do.