The default is 1 day. I am not sure we have a 'recommended' value. In terms of the passivation data, it should be cleaned up if certain conditions are met. If you see old passivated requestors not cleaned up, you should really pursue the root cause. If that is the case, create a SR to further investigate.
We created Dynamic System Setting : initialization/persistrequestor/contentExpiryThreshold with the value of 36000. (10 hrs) and continue to monitor if the Passivation Data temp directory being cleaned up.