17 February 2017
The fps setting in UI affect input rate for frames. fps of exported video is fixed to 24 or 30 fps depending of output format. The software drops unnecessary frames automatically during export. Or it may repeat frames if fps is below exported video fps.
Even 60 fps may not be enough, we recently received feedbacks about it. One may calculate interval incorrectly and make camera shots too often. Now you have choice to drop every 2nd frame manually or set fps to 60 and software drops it for you.
If input fps is above 30 then an exported video is more or less smooth, For low fps software does not make any interpolations for intermediate frames thus it may not look smooth enough.
If your SSD and CPU are fast enough then the preview would work very well to quickly evaluate how fps setting works.
Hope this helps!