I'm not sure how much of the cancer reduction you could get from taking D3 and not getting sunlight.

My vague and untrustworthy impression is that D3 supplementation is better than nothing but has risks related to calcium going to the wrong places, which may be mitigated by Nitric oxide which is also sun linked, and might also be mitigated by not being K2 and magnesium deficient which most people are. I should probably start being better about archiving what I read so that I can stop being vague and untrustworthy.

The effect isn't large enough to be noticeable.

I do notice a muscle and general relaxation effect which is deeper and lasts longer than, say, an equally warm shower. A blood panel I got back when I was not supplemented said I was pretty severely D deficient, so it might be that I feel the effects more. (Though from what I know of the biology of this the NO is more likely to be responsible for the relaxation effect than the D3.)