I wash my cookie sheets constantly, because I use them for a lot more than baking cookies. In fact, I quit baking cookies years ago when I realized that only maybe 2 out of every 5 cookies made it to the cookie jar.
This afternoon I baked 2 pounds of bacon on two of my cookie sheets. I drained off the bacon squeezings and they're now soaking in preparation for a good scrubbing. I usually wash them by hand but sometimes put them in the dishwasher if they're dirty and I've got close to a full load. Right now the dishwasher is empty, so they get hand scrubbed.
Life is much more manageable when thought of as a scavenger hunt as opposed to a surprise party - Jimmy Buffett