If you and your real estate agent suffer from poor communication, then the relationship between the two of you can deteriorate at a rapid and rather ugly rate. The agent can start getting impatient, you can get frustrated, and things can just start really going downhill. The agent may even start thinking that you have no plans to actually buy or rent a home.
This is one vital reason to make sure that you choose a real estate agent whose personality matches yours: so that you can be completely honest right from the start. If you tend to be impatient, you have to feel comfortable enough to tell the real estate agent that.
If you tend to worry a lot, if you have a lot of questions, or anything like that, you have to be comfortable enough to disclose all of that information.