Saw blades and wire sort of defeat the purpose of a string trimmer being able to get next to fences and buildings without causing damage, and still sometimes they do. The saw blades normally don't work well for grass, the blade tends to not throw the grass and you just get a clump and a mess, they do great on small saplings. I just forget about the automatic trimmer heads that don't ever seem to work and advance the string manually when needed.