Double ropes are often used for ice climbing because they offer lower impact force in the event of a leader fall, hence are less likely to pull out ice screws. They also come in handy for rappelling ... on many multipitch routes the descent is essentially to rappel back the way you climbed.
Some times on certain climbs usally mixed climbs they come in very handy when going from rock to ice .If i can find some pictures I will show why, if you have done much mixed climbing you would see why they come in handy.
When I can I will send you stories of climbing adventures if you want them. I just have to slow down a little and get some wrote to you . I am proud of you moving on to the next hard lead. i have been climbing since 1973, and motivated to start thinking and finding out about climbing since 1963. I watched two German climbers in 1962 and that got me on to thinking climbing. Have not stopped since . Thanks for your comment I enjoy your adventures and pictures on summit. I will stay in touch Best of luck on the rock and ice.