Peripheral illumination correction in camera

Is there any reason not to use the peripheral illumination option for my Canon lenses? Does it have any impact on resolution? I have used it with my 18-55IS, because of heavy vignetting without it turned on. With my EF lenses, I haven't noticed big vignetting on my crop cameras.
On or off? What do you think?

Why not leave it off and shoot in RAW. It can be added and adjusted easily in post, if necessary.

Except in extreme cases, none of which I can think of ATT, vignetting on a crop-sensor using an EF lens is not an issue. I haven't seen that using the peripheral illumination correction with an EF-S lens causes any resolution problems. The 18-55 IS is kinda soft on the edges, at least the one I used to own was, so any degradation you see might not be caused by peripheral correction but by the lens itself.

I second rrblint. Shoot in RAW and correct deficiencies in DPP.

When used fully open, there's a noticeable vignetting when using the EF-S 17-55 mm f/2.8 IS USM wide open.
Since peripheral correction brightens the corner areas, there's a risk for more noise in the image. As there always is, when you boost exposure in post-processing.