The same person becomes three people
One guest books under a nickname at one concept, a work email at another, and a partner’s phone number at a third. In a spreadsheet those are three rows. They get three copies of the same email, and none of them reflects what you actually know.
The export is stale the day you pull it
Every segment is a snapshot. A guest who came back yesterday still shows as lapsed, and the win-back email you send them lands as evidence you were not paying attention.
Consent lives nowhere in particular
A generic email tool tracks its own unsubscribes and knows nothing about what a guest told a host in person. Compliments OS records consent per channel, checks it again at send time, and excludes guests with a reason you can see before anything goes out.
It leaves when the person does
The spreadsheet lives on one laptop and its logic lives in one head. When that person moves on, the institutional memory of your guests goes with them.