I know about nappy rash too. LOL
Best to defer the question to Patrick though I will give a general answer. I believe closing a wound in this context implies "surgical closure" of some sort -- sutures, steristrips, butterfly adhesives, "glues" etc. Leaving the wound open would be NOT closing it -- basically cleaning it out best you can and just leaving it open (perhaps with some packing -- the cleaner the better -- and pressure to stop bleeding) until it can be properly addressed. Off hand, here are a couple considerations -- nature and extent of the wound, dirtiness of the wound, the care available at the scene (is the ER doc there with his full kit?), the time it will take to receive more formal medical care. Generally, dirty wounds are best not closed until they are well-irrigated and assessed. Bites and punctures would probably almost never be closed on the scene. They also require specific antibiotic treatment depending on the animal or in the case of a puncture -- what it was and did it go through a sneaker (nasty pseudomonas lives in the "rubber" sole). If you must close a dirty wound, you want to open it back up in controlled settings as soon as possible, REALLY irrigate it and take any further action that might be necessary at that point. Just a couple examples. It's much more complex than this. Bet Patrick would be keen to take this on! Would be interested in what he has to say! And of course, his kit!
Did a winter hike in Tasmania -- met up with an Ozzie ICU specialist who brought next to nothing in terms of a medical kit -- Tegaderm for blisters and some Panadol maybe. Note: he had 50+ lbs and lots of camera equipment so I doubt he was attempting to save weight. He had some nasty stuff going on in terms of blisters but refused any of my quality blister supplies out of pride, I suppose. Admired my collection but refused to take any. We only had 2 days left, and I had a week's worth -- I had needed none. I left them out that night -- hope he snuck some. After all, he spent about 3 hours building a fire from wet wood and fuel blocks so we could attempt to dry stuff while I curled up in my bag with a Nalgene bottle of hot water. He was with another bloke and I think he was keen to show off his fire making skills -- lined up all the materials like he was doing a medical procedure and then proceeded in a very orderly fashion. Works for me!