Storage capacity exceeded

I have some problem with storage capacity in my Dynamics 365 (Online) CRM and I am not sure about the real cause of this. I see that I exceeded the capacity over 40% and on power platform my global admin shows me that most of this space taking the attachments. My first thing it was an attachment in emails which are sent by sales agents, but I am not sure about it. What other attachments can take up so much space?

Our system supplier suggests to use Azure Blob instead of ordering additional space on Dynamics because of costs. What do you think about it?