Many, at least in the US. It's not just companies, government agencies also have similar needs due to sunshine and open-access laws.
The alternative to having a document retention policy is to just have employees delete things in an arbitrary manner. It's not just CYA for leaving inconvenient doc lying around, it's also to ensure the proper retention in the event of a preservation order or public records request.
Some companies go way further than others. One place I worked included "notes of a personal nature (eg, birthday cards)" in the retention policy and let us keep them for a week or two before destruction.
That's weird, my company has the opposite policy. Nothing can be deleted. Employees can delete emails on their side, but the server keeps a copy of every email indefinitely in a "vault". That's for legal purposes apparently.
Most Fortune 500 companies have a document retention policy that every employee needs to read the generic training video/documents on when getting hired and agree to.
This sets a general policy of deleting documents/emails/etc after $X days. This is really a CYA policy to purge old conversations if a big lawsuit comes down asking for document retention in relation to some scandal, and if its older than $X days you're covered since your standard legal process was followed.
