Floor limits have become less significant as credit cards & most of the debit cards started being processed electronically, and all transactions are typically authorized online by sending the Authorization request to their issuing banks.
Floor limits were of more significance when most credit card merchants processed transactions by taking a physical imprint of the card rather than electronically swiping the magnetic strip, and obtaining an authorization required time-consuming human intervention.
With modern card readers, most merchants and banks will obtain an authorization even on very small charges, as it costs little to do so and helps protect against fraud.
[1] If a store has a floor limit of $30.00, a purchase costing $29.99 (or less) would not need to be authorized by the customer's bank through Online transaction at that very moment.
However, a transaction of $30.00 (or more) would require Online authorization at that very moment to confirm that the customer has the necessary funds available in their bank account.