In most cases a wee bit of 'lip' is involved. The police, wrongly, think that taking them down to the station will teach them a lesson.

If the police in anyway prevent you going about your daily business then they have 'arrested' you. I have said this before, you should only be arrested if;

You are likely to continue the offence.
You are a danger to yourself or the public.
You fail to give your proper name or address.
The offence is of such a serious nature that you are likely to be sent to jail if found guilty.
You are under age and your parents have to be contacted
Plus another couple of reasons that I can't remember.

You should not unwillingly be taken to the police station to 'help them with their inquiries'. Why should you need to help them with their inquiries, that is what THEY get paid for.

Why don't they catch more murders? We all know that murderers have coats and jackets over their heads.