Site Collections or Subsites with SharePoint Online

Which is better Site Collections or Subsites?

I proposed to structure: - all teams under the /teams site collection managed path, so 1 site collection per team - all project/collaboration sites under the /sites managed path, so 1 site collection per project site

I've been overruled by my team who want just two site collections and subsites to hold all the team sites and site collections.

My main reason is keeping the security groups clean and not cluttered. Also keeps things nice and simple.

Downside I can see is branding changes will be difficult across many site collections but I'm sure there's a powershell script which can do this sort of stuff.

Remember: This is SharePoint Online not on premise.