Collecting the day-of information
It's important to have a clear check-in process day-of so you know who is attending. This data is valuable for your team and stakeholders in your event. For your team, it gives you a clear demarcation of who actually attended the event and finally who submitted. These stats help you know what exactly has been the reach for your event. For the sponsors, this data is again highly beneficial to know how many people actually got to know about their offering vs how many utilized them.
If you have already gathered all the fields you need from attendees, there a ton of ways to gather check-ins. If you missed a data category like address or age at registration, you can use check-in as an opportunity to get that info.
Check-ins for physical events are important to make sure you know who is at the venue. Having lanyards, wristbands, or nametags can help identify who is supposed to be at the venue, and also help put names to people who meet at the event.
Organizers can have volunteers set up at table/s depending on the size. Make sure to have plenty of space for a line, and that it is spread out enough from sponsor tables that the area will not get congested with the initial flood of hackers.
Have a way for the volunteers to verify the attendees have registered. A simple ctrl+f for the name in a google spreadsheet with a column to mark with an X is an easy way to set up check-in. Have assorted stickers/swag hackers can grab while volunteers are completing the check-in process. If your event requires school/state ID to verify identity this would be the time to check.
If your hackers need to write down their name have a table or two with lots of sharpies on the side that they can go to after they check in. Some hackers may take a bit more time for this step (especially if their hands are full of stickers/swag) and you do not want to clutter up the check in lin.
Consider having a separate form for late registrations, even if they have to wait until after all preregistered attendees have had time to check-in. Everyone checking in should still complete your full registration form.