The clause exists to stop a seller from waiting out the listing term, then closing privately with a buyer the agent already found and showed through the property. It only applies to buyers the brokerage can document introducing during the active listing, not to every buyer who shows up after the term ends.
Length and scope are both negotiable before you sign, not fixed by regulation. Ask for the exact number of days the protection period runs, commonly 60 to 180 days, and ask for a written list of every buyer the brokerage considers introduced, updated regularly, so there is no dispute later about who counts.
Joel Dyck explains the exact protection period and the buyer list in plain terms before you sign anything. Get your hand-reviewed valuation from Joel Dyck.