It depends (as always, right?) on what you’re trying to accomplish, and what your current Gainsight configuration is. Here are a few guiding ideas, though:

• Building a Playbook on a Global level means the Playbook will be available to both Company and Relationship records. If you build on a Company level, the Playbook will be available to Company records, but not to Relationship records.
• If you’ve not configured Relationships now, and have no plans to use Relationships, then it sort of doesn’t matter. As a best practice then, I recommend building on a Global level. This future-proofs you some, because if you ever do deploy Relationships, your Playbook will be available “as is” without further reconfiguration.
• If you build on a Company level, and then later deploy Relationships, you may need to rebuild or replicate your Playbooks so they are also available to Relationships.

More here:

https://support.gainsight.com/Gainsight_NXT/04Cockpit_and_Playbooks/00Cockpit_Horizon_Experience/Admin_Guides/How_to_Create_Playbooks#Playbook_Levels