Overlay How to?

What is the correct way to add overlays (scratches , dirt, wipes, smudges, water droplets, hand prints, finger prints etc).

Should I add it with color or roughness values? All these overlays uses the same method of uses different techniques?
Or is there a best way to do that?

None of the above. You are adding imperfections to a surface. So you need the imperfect surface and the perfect (for want of a better way of putting it) surface. For smudges, wipes, prints etc, mix the imperfect with the perfect and use your smudge etc. texture as the factor.

For scratches, that will be a bump - unless you can convert to a normalmap, in which case a normal.

Sometimes, you need to use both.

Start here: https://www.youtube.com/watch?v=lYO_gFh1RCc

For the record, if you have your textures, ignore Andrew’s marketing aspect. The method doesn’t rely on paid for textures - you can create them yourself.

Thanks Roken…I will keep this in mind…