I have never sharpened my blades as much as many members here seem to (once a day, or every second day), usually only once a week or every 2 depending on use. Does the fact that many of you are running z's at high speeds mean that sharp blades are more important.? We run WB's (and walk behind them) & 21's on small residentials so we are moving alot slower than a Z in open area. Are razor sharp blades less important in these conditions? Does the blade tip speed compensate for razor sharp blades at slower cutting speed?