The reason to offtopic talk can be that may be not all people who join the channel may be a fan nor has a lot of knowledge on the chat room topic. They are either lost and end up joining that channel, have their friends there or just want to take that resentment of anything out of their system. Let’s face it you cannot talk about a particular topic for hours until and unless you are a massive fan.
One of the reasons why people prefer offtopic talk is to either get to know some girls, their personal information to later on find them. A lot of my friends became a victim of this prick where they told a guy they met in a chat room where they lived, where they studied, their real name, almost everything and that guy ended up in front of their classroom. Especially a girl should be more careful around people like these. Keep your guards up if someone starts an offtopic talk with you. Do not give out your personal information over a chat room private or the main page it would really get you into trouble.
The measures taken to keep a topic oriented chat room clean from any offtopic talk is to have an active operator in the channel at all times. The duties of an operator of a channel is to keep the channel clean from any dirty or offtopic talk, flooding, DDOS or fights that people pick up on stupid things. People usually get kicked if they are having an offtopic talk on the main page or even in private. Some are banned if they just won’t behave and respect the rules and regulations of that chat room. One should be careful in a chat room too where people send each other viruses or infected files to either hack into your computer or install a key logger. They may be people who you might know but as IRC or any chat room service does not include scanning files that are being sent and receive so you have a lot of chance of getting infected. Avoid accepting any file that you may get even from a friend. Chat rooms are a place where no one can be trusted as it’s pretty easy to lie and not get caught.
The thing to remember while entering a chat room with a topic is to avoid an offtopic talk over the main or in private, do not give out personal information to anyone at any cost for your own safety, ignore any messages you receive to download a file as it can be a virus, spyware or a Trojan, if someone is having an offtopic talk or forcing you to have one inform this to the operator of the channel right away and he or she will take care of it themselves. So when joining a chat room just have fun, stick to the topic and relax.