doc/manual: replace bad advice about package options and overlays (#371513)

nixos/doc/manual/development/option-declarations.section.md

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 Creates an Option attribute set for an option that specifies the package a module should use for some purpose.
 
-**Note**: You shouldn’t necessarily make package options for all of your modules. You can always overwrite a specific package throughout nixpkgs by using [nixpkgs overlays](https://nixos.org/manual/nixpkgs/stable/#chap-overlays).
+**Note**: You should make package options for your modules, where applicable. While one can always overwrite a specific package throughout nixpkgs by using [nixpkgs overlays](https://nixos.org/manual/nixpkgs/stable/#chap-overlays), they slow down nixpkgs evaluation significantly and are harder to debug when issues arise.
 
 The package is specified in the third argument under `default` as a list of strings
 representing its attribute path in nixpkgs (or another package set).