For both the scenarios the answers to the questions will be similar.
Below point necessitate cache clearance
1. You're installing pega hotfix and as part of the installation procedure it is required to clear the cache.
Below are some of the points that necessitate restart
1. Specified as part of hotfix procedure.
2. Any changes to JVM arguments as part of the delivery.
3. Any changes to DSS which will take effect only after restart.
Many projects have it in their procedure to do a server restart post deployment due to cache issues faced in earlier versions as part of deployment in multi node environments.
Ideally server restart or cache clearance for just ruleset import or dB changes are not required.