101 characters: let the other fields do the rest
Facebook's intro bio is one of the shortest profile fields anywhere. The rest of the Intro box already shows your work, education, city and links, so the bio does not need to repeat any of it.
Use it for the one thing those fields cannot say: what you are about, or for a Page, why someone should message you. The generator keeps every result within 101 characters; if you add a line break, check how it looks on your profile, since a break leaves even less room per line.
Personal
Teacher, trail runner, terrible at gardening. Usually in the Peak District on weekends.
Local business Page
Family bakery in Leeds. Custom cakes to order, message us to book a date.
Creator Page
Easy weeknight recipes, new video every Tuesday. Message me for collabs.
Profile intro or Page bio
A personal profile bio is read by friends and people who look you up, so it can be personal. A Page bio is read by customers who found you through a post, an ad or a search, so it should say what you offer and how to get it.
If you run a Page, the most useful last few words are an action: "message us to book", "order through the shop tab". Those messages land in your Page inbox, which is where the next step happens.
When the bio says "message us"
SociaHive can answer Facebook Page and Messenger messages for you. If your bio asks people to message a word like MENU or BOOK, a flow can reply with the menu, the booking link or a question to qualify the lead, at any hour. SociaHive also schedules your Facebook posts, so the Page the bio sits on stays active.