What does the "Set a maximum number of random recipients from targeted segment" mean?

On the Contacts step of the Create a Campaign Workflow there is a blank box titled "Set a maximum number of random recipients from targeted segments" (seen below).

You can use this setting to limit the amount of recipients receiving a campaign (as opposed to all contacts in all segments assigned to the campaign).

Notes

1. For Campaigns with multiple segments, the "Set a maximum number of random recipients from targeted segments" applies to each segment, NOT the campaign, and therefore not the cumulative total of recipients from all segments.
   
   
2. This option is not available on Split A/B campaigns.