There are standard poker rules for games, but professionals and players who have a long history of playing Poker behind them don't follow these rules. Like professionals in other fields (the blackjack counting cards players for example) who know their stuff they make up their own rules and do what it takes to win. If you ask a professional player about the rules of Poker he will tell you there are only two rules. One is Win all you can and don't cheat.

A professional will use poker rules in order to provide fair and acceptable resolutions to problems which might occur during a game. It will give him a advantage because it reduces the bickering over a rule and saves time. The number two reason is that it will help other players to accept intricate games and difficult game modifications. Knowing the rules will help the professional keep his hold on the game this is the third reason. The fourth reason is if he is not reasonable and does not project his image as a fair player then less experienced players will tend to avoid him and he will not get to play as many games as he likes. This will also increase his image as a judge of the game and other players will look up to him to resolve all kinds of issues. The last and the main reason is it will also give him a chance to make and control the rules which will help him in his main goal of winning as much as he can without cheating.

In any case in private games Poker rules are not written in stone and are not followed religiously, because Poker is not a game with strict rules. If you follow rules in a rigid manner or rules which are published by Hoyle the book of rules , a player will get stuck while deciphering the different situations which arise while playing the game, this will delay the resolution of these problem and the result will be less control of the casino rules by the player.