Most of my neighbors (as do I) vent the garage door during the day and evening. And like BillZ, only a bit to hopefully prevent a not so honorable person from crawling under or leveraging up the door.
You might want to verify that your garage door locks when partly open. I just replaced my openers after I found that you could just lift them when closed. The guy who came out to do it said there is a locking mechanism on many that clicks in (or should) when the door is fully closed. So, in many door designs the door *only* locks when fully closed. So go out and give a big pull on your door when partly open to see if your opener allows for locking when partly open. Otherwise you might as well have it fully open.
-robert