Some of the things simplify3d does that I don't think prusaslicer does. Or if it does - I can't figure out how :-)
And possibly the reason to get s3d.

Processes. A process in s3d is essentially a collection of settings that you apply to your prints.
PS does that.
But s3d allows you to have multiple processes either applied to a single model, or different models on the same build plate can all have their own processes.
Printing two things ?
one is detailed and needs to print at 0.1mm and slowly, while the other is basic and will print fast at 0.3mm.
Just use a different process for each object and you can printt hem both at the same time.

It is really useful. I often applky different speeds and layer heights to different parts of the same print.
Printing a bracket with a few fiddly bits. Just use different processes for each part.

As i mentioned - different printers can all have their own processes. Different filaments likewise.

It's a biggee and something I would really miss if I had to use a different slicer than s3d.