Choosing a new home is an emotional process. You want buyers to feel as comfortable as possible when they view your home. This is why you should not be present when the realtor shows them your property.
When the owner is present, buyers often feel like intruders and feel rushed to leave. They also don't feel free to ask questions or express concerns. You may be tempted to remain home in an effort to answer questions or provide information, but buyers are typically more comfortable obtaining information indirectly through their realtor. Your presence also inhibits honest feedback, which can be crucial for future showings. If something specific is turning buyers off, you want to know about it.
For best results, vacate the premises during all showings of your house. This gives buyers the freedom to explore and enjoy, so they are more likely to fall in love with your home.