Recommended · for some experience
To Pour or Not To Pour | Copper Pour in PCB Design
Why people recommend it
Zach Peterson's Altium Academy talk is pointed to by board designers weighing whether unused outer-layer areas should be filled with copper.
Watch for: Suits people already laying out their own boards
In their words
There's an Altium Academy video in which Zach Peterson addresses your very question: "To Pour or Not to Pour | Copper Pour in PCB Design".
JYelton on electronics.stackexchange.com, Feb 2023. CC BY-SA.