With current Access Grants setting, downloads can only be limited by time.
However there are plausible use cases where a limit by the number of downloads would be a better fit for a customer.
Example use case could be a media professional who uses Tardigrade to make one of his movies available for a festival to download but is not interested in spreading his work further.
In such cases a limit by the number of downloads is an additional security step to make sure that a file can only be downloaded for a specific intended purpose.
Another reason for a limit by number is cost control. A time limit does not limit the number of downloads, thus if a link gets spreaded in an unintended way, it could result in hundreds and thousands of unwanted downloads which the customer would have to pay for. If a user can set a download limit, he can limit this financial risk very efficiently.
As last point if you look at sharing websites it is very common in the meantime that downloads can be restricted by the number of downloads, so the requested feature might simply be expected by Tardigrade users.
In a perfect world a user would be notified by email when the limit number of downloads has been reached and then he would be able to set a new limit, reset the limit or let it expire or maybe even switch between different limit type (time based / quantity based).