Five years ago I bought a used Model 77 Skilsaw. I've used it for a bunch of house projects, and it's very versatile. I noticed that it was starting to be more work to cut things and I was getting some burning and smoking, so I decided to put on a new blade. Here's the last cut with the old blade:
And the first cut with the new one:
You can see that the old one is much rougher, where the saw has torn its way through the wood. The rings are raised, because the dull blade has torn out more of the soft earlywood the harder latewood. The edges are splintered and there are burn marks. On the other hand, the new one is smooth, because the blade was sharp enough for a clean cut. No burning, minimal splintering. It was also a much quicker and easier cut.
Mostly this is to say, sawblades are not that expensive or difficult to change, and I should have replaced this one sooner!