What are the disadvantages of using a retractable fishing rod?

First of all, your going to lose sensitivity which is a major drawback if using lures, since you'll want to feel the lure twitching on the bottom and if using bait you will not be able to detect any slight bites such as when the fish simply "sucks" the bait in as opposed to running with it. Secondly, the integrity and strength of the rod is likely to be compromised because of the increased week spots from so many jointings in the section. Lastly, the multiple sections will turn once you hook a decent fish or get snagged, causing the line guides to misalign. It just means more time spent getting it all squared back up. If it is indeed going to be solely used for backpacking, it would be a good choice. However, look into a one or two piece for regular use, you'll enjoy it a lot better.