As I was showing houses this week, we arrived at one of our appointments to find the homeowners still home. This made my clients uncomfortable so we skipped that particular home. Some buyers wouldn't care and would actually welcome the chance to ask questions directly to the homeowner. This can then, in turn - make the homeowner uncomfortable. I have had sellers tell me "This is my house, i'll do what I want". And that's true. It's your house. But aren't you trying to get someone else to buy it? Buyers will sometimes remark "that guy was rude".
The reason Realtors tell their clients to leave the house and take down things like pictures and collections is an important one. From the moment those buyers pull up in front - they are thinking of this as their next potential home. As soon as they see the homeowner - it becomes someone elses home. Sometimes the response I get from sellers is "They aren't going to not buy my house just because I was home". True. But most times the decision to buy a house is an emotional one. We fall in love with our house, we can see ourselves living here, I can see the kids riding the bike up and down the block. Many suddle things can influence a buyers decision - so it's important to given them every advantage. Put away the pictures, go next door to the neighbors during a showing or take a drive. Yes, it is your house. But do you want to keep it that way ;)