I get this question from my clients all the time! In my opinion, if you can spare the cash, I would always buy a locker when you are buying a condo. You can always use the extra space or rent it out! It is the one of the best return on investment! Typical locker rents out for $50-75 a month. Maintenance fee on a locker is usually $8-12/month. Cost is usually $3-5k. Consistent Return on investment per year = 10-15%!
But remember, lockers must be registered to a condo, so if you sell your condo you must sell the locker with it or sell it to someone else in your building and have them register the locker to their unit.
Msg me if you have any questions!