Lodge 4 qt

Just picked up a NIB Lodge 4 qt. A little rust on outside but clean on inside. Waiting for warmer weather before I clean it up and reseason it with Beeswax. Sold on that treatment. But I do have a question. I have a generic 6 qt that I've been learning to cook on. I thought it worked fairly well with everything I cooked in it being done and tasting great, but has a loose lid. The Lodge is very tight fitting which I suspect is a good thing. But what's the problem with a loose fitting lid as long as ash and dirt don't get inside from what's been sizzling on the lid? The build up of steam and pressure is going to make even a tight fitting lid like my new Lodge dance up and down at least a little as the steam and pressure escape. At least that's how I am figuring how a DO works, they aren't a pressure cooker. I'd like to hear the reasoning why everybody seems to be blasting loose fitting lids.
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