What is BigTime used for?

As an architectural business, we use Big Time to log our time, usually in 15 minute intervals, showing how much time was spend on each task, for each phase, of each job. We have some employees that only work on 2 or 3 different projects while others may log time to 15 or 20 different projects. We use this information to accurately big our clients each month. We do our invoicing through Big Time as well