A Lost & Found game might have just one Playbook, or multiple Playbooks for different Object archetypes.
If you've only got one type of Object in your game, Playbooks are a simple way to bring all the relevant content into one place.
If your game supports more than one kind of Object, grouping content into a Playbook lets you create a tonally-consistent experience for each Object. You can tailor each aspect of the Playbook (Creator, Traits, etc) to be specific to that Object, making them feel distinct from one another.
In Artefact, where Objects are different kind of magical items, there are nine Playbooks. E.g. The Weapon, The Shield, The Instrument, etc.
The content that makes up a Playbook doesn't need to be entirely unique for each Object in your game. You might repeat certain key questions, or they might share some or all of their suggested Traits.
Deciding how many Playbooks to include with your game is a question of variety and scope:
Within the broad category of Objects your game is designed around, how many distinct archetypes do you think there are? In Artefact, the nine Playbooks all represent magical items, and (for example) a Weapon is clearly different from an Instrument in some fundamental ways that the game wanted to represent. But the difference between different kinds of Weapons (e.g. axe, sword) was not considered great enough to warrant unique Playbooks.
Also, of course, there is no hard stopping point for how many Playbooks you might create—but at some point you'll run out of time, money or interest!