Or in other words, does the lens correction do ANYTHING if i only shoot in raw?
In terms of the images themselves, all it does is set flags in the metadata that DPP recognizes, and it would then apply those corrections on your computer. If you use another RAW converter, then the in-camera corrections will not do anything to the RAW image. They will be applied to the JPG preview image that's embedded in the RAW file, though, and it's that JPG that you see during image review on the camera (and also the histogram data, although lens corrections shouldn't affect that, Picture Style, ALO, etc., do).
I tried to verify that DPP made the corrections based on flagged settings, but could not confirm that with my 5D MK III. Corrections were turned on in camera, but DPP did not apply the corrections to the raw files.
I manually applied them, and then the size of the cr2 file more than doubled after I saved it.
The corrections were applied to jpg out of camera images without any noticible increase in file size.