It surely would help to disable resampling — if input and output frame differs. But with equal frame rates there usually is no need to disable resampling (which then causes frame drops or frame doubling).

I think it was showing the slight difference in frame rates by resampling. Perhaps most people never have this problem because their cameras do not distinguish between 23.976 and 24. I know many cameras call 23.976p 24p. The LS300 actually does the different frame rates. At any rate (no pun intended) it stopped the doubling of image.

Maybe you oversaw my first post after I edited it.
While in Vegas Pro there are a couple of render types which really only offer 23,976 fps output and no 24p (P2, XDCAM EX, XDCAM HD MXF, XAVC), many other render types also either offer true 24p by dropdown list selection or by simply typing the value "24". ProRes, Magix AVC, MainConcept AVC, Sony AVC, Intel HEVC, MPEG-2, HDCAM SR, AVI – all of them offer true 24p output.
And if you select one of them for your output, you don't need to disable resampling.

I didn't notice the drop-down list in customize render and was using only the properties customize and since all of those render types default to 23.976 it was using that. Disable resample accomplishes the same thing for all render types simultaneously, as I tried rendering several different file types and they were all good. I have not yet seen what good smart resampling is - can you explain that? Another example of a problem with it - I was converting interlaced avchd to progressive XAVC at a different fps - 29.976 interlaced to 24p. The smart resampling wrecked it even when progressive was selected and the shot was played at a different rate (80% if I remember correctly - I have it stored as a project file). But as soon as it was disabled the conversion was perfect. So I am curious as to what smart resampling is ever useful for.

Using or avoiding resampling most often just is a matter of your personal choice.
Resampling avoids frame dropping and frame doubling when changing the frame rate. How much this would be visible depends on the movement of the footage and the size of the step it takes to go from one frame rate to the other.

Without resampling and going from 24 to 23,976 fps, it will drop one frame each 42 seconds, so there might be a slight jump visible each 42 seconds (dependend on the movement of your footage). With resampling enabled there won't be a jump because all the frames needed are re-calculated (but this is done by a simple frame blending in Vegas Pro which introduces ghosting effects).

Without resampling and going from 50 fps to 30 fps, it would need to drop 20 frames each second. Again resampling would re-calculate these missing frames by frame-blending.

So sometimes one would select resampling for the sake of smoother motion, sometimes one would disable resampling for the sake of clear frames.