Using the same blades for a couple of seasons now and they still seem to cut fine, but starting to wonder if I'm just not noticing the dullness. Read that sharpening once a year is a good rule, but also seen people say they replace them every season. What do you look for when deciding if it's time to swap them out? Is it worth sharpening, or do you just buy new ones? Heard that uneven cuts and frayed grass tips are signs, but not sure if that's always obvious. Would appreciate some practical advice from people who actually do this regularly.