It’s all about context. If you write a convenience function and put it in zshrc, scripts you run from the cli will not have access to the function as defined in zshrc. Same with aliases added by zsh plugins etc.

If you need “the thing” on the command line, zshrc. If you also need it in scripts you run from the cli, toss it in the profile file.

ETA: I personally keep the functions I want to access from scripts in .zshenv as I recall reading that this file is ALWAYS sourced.