As opposed to Inverse Assignments?

The Company has a business to run. Would you rather the pilots who want to fly (and who's seniority potentially pays them more) fly, or the junior guys who somehow managed to get a day off they wanted forced to do something they don't want to do?

Having worked for a company that junior manned you every year to get through the holidays and weekends, green slips beat the alternative. Also, junior manning can result in sick call issues. People don't call in sick, even when sick, during their off days. If junior manned you can find yourself having to explain a dubious sick call.

Always better if the people who want to fly, fly, and those who don't enjoy their time off.