Need to keep your leads inactive? Use Pending Leads.
Typically, leads are in one of four statuses: open, won, lost, or canceled. It's possible to place a lead into a pending status, this is typically only done when importing many leads.
Pending leads are not assigned to a user, nor do they have an attached sales process. They're designed to fit the workflow of importing thousands of leads, then slowly 'thawing' smaller numbers of leads. Use the bulk edit tool to convert pending leads into open leads.
When you use the bulk edit tool to open a collection of pending leads, those leads follow your standard rules for assignment and process selection.