I agree with
@Vaughn. It depends so much on what process you're talking about. Then it also depends on what look you're after, what kind of raw paper base you're using, what kind of chemical interaction effects you may or may not be having, what the situation is with sensitizer absorption or pigment staining, etc. etc. etc. etc. etc.....
Keep also in mind that sizing is not the only way to do something with surface finish; you could also apply a top coat over your image. Waxing has always been fairly popular, but other top coats are also feasible.
Don't regard sizing as something you have to do because 'people' say so. It's something you use to solve a particular problem or to obtain a particular effect. Nothing wrong with experimentation, but this is a particularly deep hole to fall into if you go into it without any direction.