At least two, but many if it doesn't add too much complexity to use as a good self-teaching tool. More just to show that millis() can be used to track multiple time intervals used by multiple processes within a sketch. I just think the existing blink without delay example sketch is 'too simple' to show off the power and usefullness of the millis() function.
Probably the main objection is that it hides the "real" technique behind a library, but then don't most low-level functions do the same thing? For example, delay() itself. (OK a function rather than a library, but there are time you don't really need to know the low-level detail).
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