I think it would helpful to the clan leaders to be able to promote a trusted clan member as their lieutenant. This person would be able to help with challenges(I.E. make challenges, accept, start, bounce and decline them).
They would also be able to moderate the private forums as well. They would not be able to kick anyone out of the clan, or change the name and logo, set up leagues, etc. That power would remain solely with the clan leader. Running a clan can be a big job for some of the leaders of the rather large clans and even the smaller ones. This may take up some of their precious time they want to devote to their actual games. Being able to promote one trusted member to help with clan operation I think would help to increase clan activity and provide more competition.