Just to add to what's been said, if you have a refractor and want to create diffraction spikes in you images you can use fishing line across the scope objective (or over the dew shield).
I've used clear, medium thickness, line in a 'cross pattern' held in place by blu-tack or sticky tape, only need one cross.
You get a nice effect and no need to do anything in post production.
Like Al said, it's up to the individual, some like them others don't.
