I'm trying to figure out if deploying/upgrading solutions and activating features recycles the app pool or interrupts/slows the user's actions in any way. I need to know if these steps can be performed while there is load on the server, or it is best to do an after-hours deployment.
The specific commands I'm using upgradesolution or displaysolution, addsolution, installfeature and activatefeature, but for the sake of completeness, it would be nice to have a comprehensive list.
As a general rule - always do feature / solution upgrades outside of hours. You never know how the change will affect the running application.
The reason activatefeature doesn't is because you are executing the commands contained in the feature e.g. events and schemas. All the others are registering assets for use by sharepoint so require a restart.