OSA is a censorship law that pushes the cost of monitoring and compliance onto website operators.

This means that unless you are a gigantic corporation with deep pockets and can afford all the hundreds of hours of lawyers, developers, and moderators needed to comply with the law then you really can't afford to operate websites that other people can use.

It is effectively handing over the keys of WWW to mega corporations in the UK.

If you are operating a personal website it doesn't impact you, but if you are doing forums or anything were more then a handful of users use then you'll need a pretty significant budget to keep it running without the fear of the government cracking down on you.