Rotating or sticky sessions: what is the difference?

• Rotating (the default): every request leaves from a new IP. Use it for broad crawls of many simple pages.
• Sticky: add -session-<id> and every request with that ID leaves from the same IP. Use it for logins, carts and any flow of several steps.

A sticky session has no time limit: it keeps its IP while the exit device stays online. Add -time-<minutes> to end it sooner, and -const if you want the request to fail instead of moving to a new IP when the device goes offline.

The targeting is fixed when the session starts. To change the country or city, use a new session ID. Details are in the session docs.