All. The. Time. Seriously. Too often.
But the only weight I actually count is the one taken in the morning, after bathroom, before clothes, before breakfast, like you. As someone who weights herself throughout the day sometimes, I know that my weight fluctuates anywhere from 2 to 5 lbs in one day. I don't think you can compare an AM weigh-in before breakfast with a midday weigh-in after a hard workout, or an evening weigh-in after dinner. It's too many variable then.
Tattoodles did a good thread where she weighed herself frequently throughout the day and reported it. I think it's under General Diet Questions? Will try to find and post for you. It's a good example of why weight should be taken at the same time. (And I'd argue more frequently than once or twice a month, though that's coming from someone who weighs herself too much, so take it with a grain of salt

)