\item If you need to alter the frame rate, for example because different source clips have different frame rates, then recode all the necessary clips to the same future project frame rate. Here frame sizes can still have different sizes, but frame rates should be all the same.
\item Whole editing: if you need to change frame rate of some restricted part, particularly when smooth acceleration/deceleration is needed, it can be done here. But if frame rate has to be changed only due to different source fps, it is better to do it during the preparation stage.
\end{enumerate}
\item If you need to alter the frame rate, for example because different source clips have different frame rates, then recode all the necessary clips to the same future project frame rate. Here frame sizes can still have different sizes, but frame rates should be all the same.
\item Whole editing: if you need to change frame rate of some restricted part, particularly when smooth acceleration/deceleration is needed, it can be done here. But if frame rate has to be changed only due to different source fps, it is better to do it during the preparation stage.
\end{enumerate}