Just to dispel the myths, all optical systems vignette to some degree.
Saying yours doesn't, is a bit like saying gravity is a myth.
But, if the level of vignetting in you system doesn't bother you, then sure, don't apply flats.
If you are performing photometry, or simply striving for excellent image fidelity and accuracy, then flats are required.
While there are some excellent software tools that approximate then reduce all manner of vignetting and gradients, I have yet to see a better method than a properly calibrating (i.e. flats and darks) a frame.
Everything else is just noise.
