Meaning of the term "empty use" in the context of modal verbs

I'm reading a book titled Comprehensive High School English Grammar & Composition. The author, who is Indian, says this on the use of the modal verbs can and could:

Can is used to express "empty use":

1. I can walk.
2. I can feel summer heat.
3. Birds can sing in the trees.

Could is used to express "empty use":

1. I could feel the touch of cool breeze.
2. They could enjoy soothing showers.

But I'm not getting what the meaning of the phrase "empty use" is, and why the author used this term here, and whether it's a standard term or concept, or unique to this (non-native) author.

Is "empty use" a recognized term among linguists? If so, what does it mean?

Can/Could is a modal, a type of auxiliary verb that is used to indicate modality – that is, to indicate likelihood, ability, permission, or obligation.

But in 'I can smell burning', the author is really merely expressing what he smells, not his ability to do so (in the more usual usage). 'I can smell burning' is same as 'I smell burning' (although the former is by far the more usual way of expressing this, and sounds more natural). See the difference in this usage? Here, 'can' is just an extra/dummy word that may be omitted without changing the meaning. Hence, the term 'empty use' (though John Lawler's terminology is better). Similarly with the other two sentences. You can omit the 'can/could' and they still make sense.