Since the context of your question seems to be about developing models for UE4 in 3DSMax, then I think you can safely ignore using powers of 2. In previous iterations of the engine, or when working specifically with BSP, remaining on the unreal unit grid by avoiding fractional values and using powers of 2 was an effective way to prevent map errors. For models there is no hard and fast rule to utilize powers of 2 beyond that maintaining a consistent grid scaling might help make your models more modular.
Personally when using any 3d program I always set up the grid to power of two and rotations to increments of 5.625 and cylinder sides in power of twos too. Just makes things easier to attach and copy things but there is no right or wrong way its however you feel most comfortable.