What is 'use client' on all mui component in nextjs13?

I am new to react/nextjs development. Always thought react component render in server and ready as cached开发者_运维问答 to go.

But if nextjs 13 make all mui controls as client component where is the render happening?

Client side? Also as you can see even for 2 line , react way of doing it is 1000 lines.

It would download whole website/app to client mobile or desktop.

I see 260mb in my ".next" directory.

Can someone explain what portion is downloaded initially?

Nextjs .next directory size is 260mb