I have customers frequently ask me why LoadStorm has a minimum pause time. They want the load test to click from step to step in less than a second. My reply is that it is unrealistic to have actions of users like that.
People have to think about what they see, read it, make a decision, then click. Each person will respond to the delivered page in a slightly different time frame. Think time is variable because real users have a large deviation in their ability to process information. Some are visual learners, some are analytical, some are contemplative, some are driving personalities,
So when you are load testing, it will be beneficial to have a randomized pause between steps in your scenario. This will realistically represent the length of time from when a person receives a response (page) from your server to the time that person requests a new page.
I used to believe that interpolation for performance metrics was acceptable. However, now I have found that I was wrong. Especially when it comes to think time.