How often do you use diffusion filters?

[randomname]

While I've never used one before on one of my shoots, I've been doing a lot of research lately and am trying to learn more about the different diffusion filters and when to use them. Is using a diffusion filter for your shoot the norm or do you only use one when going for a specific effect? Which filters do you typically use? How do you go about deciding which to use?

Thanks in advance!