Should I be setting a base font size?

Hello, I am developing my first responise website and been trying to learn as much as I can (really enjoying the videos on YT). One thing I can't really find the answer to is if I should be setting a base font-size on the html element for rem to go off of. I know the default is generally 16px so in theory I should be fine not setting a base side right? Or is it good practice to set a base size? Thanks
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