I had a fairly minor change to some code today that modified the display order of some reports implemented as unique web user controls that are loaded dynamically based on which items you select.
I wrote out my plan and before editing any code, then I asked my co-worker, Kelly, to review it and see if it held water.
Turns out, I sprung a leak. It was such a simple mistake. The code I inherited used the Session object to store a value and my flawed plan slightly modified the values in the existing Session object. My plan assumed the web user controls executed serially, when in fact, I could not guarantee that level of access to the data in the Session object.
Sans code review, I would have gone ahead and modified the code, tested it, and (hopefully) seen the error of my ways before handing it off for final review before deployment. It would have ran without throwing an error, but not correctly. The peer review saved a significant amount of time, relative to the overall time spent on the task.
Peer reviews rock. Do them early and often!