Currently, there is no limit on how many times a discount code can be used as long as the current time of applying it is within the start and end date for the validity and the code itself hasn't been deactivated.
If a limit is necessary, you can simply create a new ticket type with the discount already factored into its price and then put values into the 'Available Ticket Type Quantity' and 'Max. tickets per user' field based on the limits you want to set.
For example, if you want to sell only 100 tickets at a discounted price and at a maximum of 2 per customer, the ticket type can be created as shown below: