Do you want to understand what is taking up all your space in Gmail? It’s easy – just use the size operator in the search box. You can combine this with the has: attachment operator to make sure you only filter for attachments, but it will work both ways.
Use a search like this to return all emails larger than 10MB:
You can also use regular numbers, like size: 10000000 for the number of bytes if you want to get even crazier. But it is much easier to use the 10mb operator. O 5mb. Or whatever.