a) You operate with a budget: Do you collect membership fees, make purchases for the organisation and generally use money in your operations? Then it is useful to register. It allows you to open up a bank account in the name of your organisation, this makes it easier to control your expenses and earnings. Registration also protects the board members from being personally liable for any costs or damages incurred on behalf of the organisation.
b) You rent or use spaces for your meetings and events: If you use spaces for your events, for example in a café or a co-working space, it is best to be registered in case the attendees of your event would cause damage to the space. You can use university spaces for meetings and events without being registered, however you will be liable for damages in case of accidents. This liability shifts towards the organisation in case of official registration.
c) You want to apply for grants:
For transparency reasons, many grants will only be able to support you if you have a business bank account. In order to get this bank account, you need to be registered at the Dutch Chamber of Commerce (KvK).
d) You want your board members to receive financial compensation for their work
UM-students can receive financial compensation for their hard work as board members of a student organisation, under certain conditions. One one the conditions is that you are an active member of an officially registered organisation. For more information, have a look at: Compensation for board members