Neglecting your time sheets
If you work for a professional services company, time sheets are very likely a key part of how your firm makes money. No reported time? No revenue to report.
In addition to the revenue issue, there is another issue to consider. Many people fail to do their time sheets because they think they are "too busy." But time sheets are a key means by which companies determine the workload of individuals and departments. If you have a team of five, and everyone is reporting more than 50 hours every week, there is a good case for hiring a new employee. If no one is filling in their sheets, you have no real evidence of the work strain on your people.
In addition, companies sometimes use a lack of completed timesheets as a delaying tactic to slow new hiring. "How can I know you're overworked if your people don't fill out their sheets?" And the ultimate hire date is pushed out at least a month. Pretty tricky, huh?
Finally, filling out time sheets is a requirement with your company. As such, it is like showing up -- something you must do. Why create a bad reputation for yourself by avoiding five minutes of work a day?
And, by the way, do them every day. If you wait until the end of the week or month to fill them out, you'll make mistakes, either by failing to report billable hours or by billing hours to the wrong client. I'd call either one fraud, unintentional or otherwise.