Everyone in your area who has shared his or her contact list with Clubhouse, in which you appear, will automatically receive a message when you register with your phone number. Even the people who are not in your own contact list.
In addition, you should ask yourself: do you want to let Clubhouse know which phone numbers are in your list? Numbers of acquaintances may not matter. But think about the numbers of your psychologist, boss, dentist, hairdresser, health insurance, bank, funeral director... Even if these people do not have you in their list, Clubhouse will still make the connection and make 'friend recommendations' based on this.
Once you've linked your contacts list, you'll also be able to see how many of your friends one of your contacts also has in their contacts list.
It's not entirely clear what Clubhouse currently does with the collected contact data fax lists (hopefully nothing, but certainly something), but it's good to be aware of.
The use of evil nudges
To ensure that you actually share your contact list with the app, Clubhouse uses so-called ' evil nudges '. Also called dark patterns. When you start your account, you are asked whether you want to share your contacts. They let you choose between 'Don't Allow' and ' OK '. ' OK ' is printed in bold and there is also a finger pointing at it. A push in the 'right direction'.