I spent the day in the woods following an excavator. He knocked down trees, I cut off root balls, he sorted the results.
I brought a spare chain and my sharpening kit. I had just figured out how to sharpen freehand and get a good result.
There was often dirt embedded in the bark around the stumps. There was a lot of dirt flying as the excavator worked. The chain went dull often.
I think I sharpened 5-6 times that day. I would have needed a lot of extra chains to keep up with that work. A file fit in my pocket, but spare chains would not.
Touching up the cutters with a round file goes really fast, now that I know how to do it. I don't think swapping the chain would have saved me any time.
I will take my used chains to a pro with a fancy machine to get all the angles ground just right, and then continue to use a file in hand to touch up in the field.