Craft's Eager-Loading Elements allows you to nicely optimize your templates by telling Craft to load everything you need in one big query.
The only rub is that you can't specify this eager loading behavior for entry, category, or product elements that are auto-injected into your template.
Eager Beaver is a small plugin that allows you to eager load sub-elements like Assets, Categories, Users, etc. to these auto-injected elements.
This is especially useful if you have pages that use Matrix block "content builders", and thus will typically result in loading a number of relations like Assets contained in Matrix blocks to render a page.