It was a big deal for us to load up and go to the local library, where my kids could pick out books to read or books they wanted me to read to them.

If you have a comparable production server in place, measuring its actual load patterns over a period of time can go a long way towards getting accurate concurrency rates and is highly recommended.

It's important for your website to load as fast as possible; users want to see your web pages quickly and if you can't give them that -then they'll go somewhere else.