llkhmeraznfoo, you bring up a valid question about protocol and/or "customary" practices. However, you'll get varying opinions about this, as you can see from some of the responses. I agree with some of the responders that you have "a right" to be in your house as long as you want to be, but if an agent is doing their best to keep one party away from another it may be to avoid any awkward or unforeseen types of issues or questions that often times surface (that could potentially affect the very sale you're expecting to close!).
If there is no other reason to be at a house other than to insure that all goes well, stay away and it'll probably go no worse or better had you been there. On the other hand, if you don't trust what the agent is saying or doing, hmmm, it may be a little late to change anything that person may or may not have done. Again, it'll probably go no worse or better had you been there... If all goes according to plan, schedule and contract, you ought to be getting a check, and the buyer the keys to the house.