I have a stack of 10" saw blades for my table saw and SCMS that have had their turn on a saw and are either caked in crud or dull, or both. Problem is, I can't tell if the ones that are caked in crud will cut better with a simple cleaning, or if they need an actual sharpening. The wear on blade teeth happens so slowly (unless you hit something foreign like a staple) that it's very hard to tell that the blade needs attention.
When do you decide that a blade needs to be sent in for sharpening?