From my days of employment at a rather large, well known and successful law firm, I can tell you how important good time billing software is to running a successful business. At the firm, it was all about billable hours. The lawyers all had to meet weekly minimums of hours. Every hour of a workday had to be charged to a client, whether they were on the telephone, face to face meetings, or in court.
Most of my other jobs did not try to attribute my time to particular clients or projects except for when I worked at the computer company. I was a multi-department manager supporting multiple government and military projects, so my time had to be allocated to specific projects. It was challenging to keep track of what I did throughout the day, but I managed.
The most interesting time-sheet I had to use was at the Franchose company headquarters. They had a complete online system that tracked your time, your vacation, and also all your expenses. I loved that program! I could access it from my desk or from my laptop while traveling by logging in via internet.
It was super easy to use and I loved getting my expenses reimbursed so quickly. Often, my expense reimbursement check was waiting for me at my desk by the time I returned from a convention or trade show. That was helpful and very much appreciated.