What kind of data needs to be passed between a CMS and a CRM?

Hi Guys,

I'm exploring a CMS integration with a CRM. New to this space and wondering what kind of data typically needs to be passed between the CMS and CRM? The CRM will have a bunch of signup forms for nonprofit space and so the CMS would be in charge of blog articles and the general website etc.

What is the disadvantage if the CMS is not integrated with the CRM?