Ever wonder what the "Same email address" checkbox is for in CiviCRM event setup? By default, CiviCRM will only let a user register once for an event with the same email address. Use this checkbox when you want to override the default.
The "Same email address" checkbox works well if you have a situation where someone, for example, a board member, is inviting and paying for several guests to attend an event. The event planner is only tracking one registrant (the board member) but allowing for the purchase of multiple tickets. This example would be done using a Price Set. This way, Tom Smith could buy two tickets, one for him and one for his wife Sally Smith. He could decide to buy two additional tickets for another couple to join them and make this transaction using his same email. The downside to this option is that you are not creating a new individual for each participant coming to the event.
Keep in mind that it is generally not a good idea to allow multiple participants to register with the same email address. Following our example of Tom Smith and Sally Smith, they will both show the same email. As a result, this would mean you could have individual contacts with the same email. In most cases, CiviCRM is configured to catch duplicates by email address. Having multiple contacts with the same email will cause issues for duplicate matching.
CiviCRM is full of many different options. Many of these options come with pros and cons so it is important to consider fully how an option will affect your use of CivCRM.