The main concerns are from granting it permissions to access your data.
As i understand it (having never used it) the biggest problem is that it can be hard to use without granting it permission to access your contacts. This is a valid concern. Unfortunately everyone you know who uses WhatsApp has likely already shared all their contacts. Combining that with other data they have got from elsewhere lets WhatsApp / Facebook construct a large part of most peoples social graph.
Still, I think best to avoid feeding them more data if at all possible. The upcoming GrapheneOS Contact Spaces feature will provide a neat way to control what contact data WhatsApp can access.
Another options you can use now is using WhatsApp in a different user profile. Maybe even worth considering using a work profile via Shelter or Insular if user profiles dont work well for you.
Imagine you can share files and images form Gallery and Files or other apps into WhatsApp so you dont need to grant Whatsapp any files / media permission. Also Graphenes Storage Scopes lets you work around those permissions and control the stuff it can access.