What problem does this address?

Looking at the Buttons block
This request seeks to provide an option for the button block to allow more options for other width sizes like 33% and 66%.
More requests for other sizes might come in so having a hook-like option would be helpful.

What is your proposed solution?

If there was a hook to add more options or even have this in the theme.json as

"blocks": {
	"core/button": {
		"widthSettings" : [ '33', '66' ]
	}
}