Buyers feel more comfortable looking at homes when sellers aren't haning around. They feel more relaxed, can take their time to look around, and feel free to discuss the home amongst themselves and with their agent. Speaking of agents, they are more in tune with what a particular buyer is looking for than the seller is. You may be really proud of your newly remodeled kitchen and feel compelled to focus on that when talking to the buyer, when what the buyer may really be impressed with is your home's three-car garage.
When a showing is scheduled, hop over to the neighborhood coffee shop for a few minutes and let your agent do the work you've hired her or him to do.