Just imagine, for a moment, that you have a hairdresser's appointment, and let's say that it is for 11.00 a.m. on any given day, we'll call that day 'Thursday', just for the purposes of this discussion.
So, you realize that there is something else you absolutely must do on Thursday at 11.00 a.m., so you call your hairdresser and ask if you can come Wednesday, instead. Your hairdresser checks her schedule and says, "Sure! You can come in at 1 p.m. on Wednesday, would that be ok?" You blow her a kiss over the phone, and hang up. Wednesday at 1 p.m. it is.
Now, I ask you, would it be sensible of you to show up at your hairdresser's at noon on Wednesday, and expect her to seat you immediately? The hairdresser sees you, and says, "My, you're early! Have a seat there and I'll call you in as soon as I can." She was able to squeeze you in at your request, so is it now the right thing to do to then hover nearby, an hour early, and haunt her? To then walk away and return several times, making your presence felt? To ask if the currently-occupied chair is going to be your chair? In other words, is it reasonable, sensible and polite to annoy the crap out of your hairdresser and her current client, making her feel as if she should rush to accommodate you?
No, it is none of those things. It is unreasonable, insensible and impolite. Yet hairdressers the world over are catering to people who are all of those things, to the detriment of the ones who are willing to wait their turn, and play by the rules.
I am a lover of rules (except the ones governing speeding). They allow everyone to know the expectations, and provide a level playing field. There is consistency, and I love consistency.
I am so glad I am not a hairdresser, so I never have to be put into this kind of situation. That would be horrible.