When to use newsletter sign up in CRM vs sign up form in Campaign?

When to use newsletter sign up in CRM vs sign up form in Campaign?

We have both CRM and Campaign modules. We want to host a sign up to our newsletter form on our website. When do you use CRM newsletter sign up form vs sign up form in Campaigns. The challenge is I need to ensure my CRM is kept up to date as master database. Please advise best option.