By default ansible-galaxy installs all roles in a single global location. If you use ansible a lot, this can lead to a situation where you have a conflict because one project requires version X of a dependency and another requires version Y. I usually guard against this by setting each of my ansible projects up to install dependencies in a local vendor directory inside the project (the NPM/composer model) using the roles-path setting.

This can be specified on-the-fly with a flag or env var, but I usually set this in my ansible.cfg before creating a requirements.yml.

[defaults]
roles_path = ./vendor/