Once partners are setup, have created users, optionally have enrolled in partner programs or have agreed to work according to agreed upon business plans, they can start selling through Sales Cloud. They can log leads and opportunities, create activities and basically work as a direct salesrep would.
That is off course if they are willing to do so. Why would a partner actually use a sales system that belongs to someone else? Maybe exclusive partners would, but most partners are not. Most partners will be resellers or distributors for multiple sales organizations, different brand owners.
One of the ways to get to use them another sales system but their own, is to reward them for doing so. That is what partner programs are for, to reward them for signing up as partners. That is the purpose of the marketing development funds, to support them in their marketing activities.
Another way to reward them is by providing them work, by transferring leads over to them on which they can work. That is what lead distribution is all about.
Channel managers can assign leads to their partners. Leads are assigned to the primary contact of each partner.
The primary contact then can reassign a lead for further evaluation, accept, qualify and convert them into opportunities to work on or reject them after which the channel managers can assign them to another partner.
I could see part of some sort of an agreement that partners get a number of days to accept or reject a lead when assigned to them. Not responding in time to an assigned lead could then be another reason for the channel manager to reassign the lead to a different partner.