Drop in is fine
I have been served there as a "drop-in" customer.
The have a decent waiting area and you normally don't wait long. 10-15 minutes, unless they are mega busy. Reservations are not required but recommended for parties of 6 or more.
You can drop in. They also wont take reservations during their busiest hours. So either way you will probably wait. I have never gotten seated right away at Spaghetti Factory regardless of how busy they are. I beleive they have a skeleton crew most of the time. But when you do get seated it flows normally.
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