Charging extra for basement "storage"?

[Jonathan Taylor Smith]

I notice on the BP Rental Property Calculator there is a field for "Other Monthly Income" and the question mark icon gives "extra storage" as a possible example of such other income...

I have a 3BR / 2.5BA Townhouse for rent @ approximately 1600SF with an 800SF partially finished basement. Sites like Zillow and RentOMeter say that my ask of $1400 for rent is near the top of the market for the area, but still reasonable for a unit of this size - and that is even without the basement.

So does the basement effectively get thrown in for free? Or is this a scenario where I might legitimately charge some small extra amount for the basement (such as for storage) - or otherwise just keep it locked off separately from the rest of the house? This may be a stupid question, as I'm not seeking to do anything unethical... Its just my first unit with a basement and its so big. And HOA / Zoning does not allow the basement to be finished into a separate multi-family unit - or I'd certainly do that!