Do I need to have all the guest names to use Table Assignments?

No, you can assign all the attendees to their tables and update the names later. If a ticket purchaser does not know the name of all their guests at the time the register, the purchaser's name will be used as a placeholder for each attendee spot. For example, if ABC Bank purchased a table of 8, but did not enter a name for each individual attending, the grid will show ABC Bank in the Actual Attendee column eight times.

You can drag and drop those 8 ABC Bank attendees to their table, and when you update the information at a later time on the Event Attendance grid, it will automatically update in the Table Assignments.