I've noticed that over the course of a week that over-working and working smarter are both self-reinforcing. To put it another way: the less I work, the less work I have to do; the more I work, the more work I have to do.
I've found that during periods where I have a lot I need to get done, I work harder. I dive in right away, take less breaks, and put in more hours. Often this is necessary for a short period of time, but it can be dangerous. By over-working the first thing that gets cut is time for reflection. By cutting this thinking time I'm less likely to see those smarter ways to get things done. I don't cut off tasks that drag, I miss an opportunity to delegate, I miss a clever solution that solves a problem. All of this ends up causing the work to take longer creating more total work for myself, which makes it more likely that I'll over-work the next day beginning a vicious cycle.
The same pattern is true for working smarter. By taking a step back from my work I review whats on my list and figure out how to cut things, I delegate early to get a project in motion, and I reflect on hard problems to find shortcuts. All of this ends up reducing the overall amount of work, which gives me more time the next day to work smarter. It's a virtuous cycle.
I try to notice when either cycle is happening to me so I can work to break or embrace it, but its not always easy to catch myself.