Channelfly, and similar features from other manufacturers (e.g., Cisco Clean Air) attempt to improve wifi performance by directing an AP to change to a different channel when it detects interference. The idea is that the AP can switch to another channel to avoid the interference, for example, from a microwave oven or even an overly crowded channel.
While this sounds good in theory, there are a couple of factors that limit its effectiveness. First, there are only 3 usable channels in the 2.4GHz band. Because the entire band is often crowded and shares the spectrum with non-wifi devices (microwave ovens, garage door openers, wireless video cameras, etc.), its is often the case that if one channel is being interfered with, so are the other two. Microwave ovens operate approximately on channel 9, where they interfere with both 6 an 11. That leaves just channel 1 as a possible substitute. There is no guarantee that it has less interference or lower channel utilization.
Second, in a large wireless system, there is usually a central controller that controls and coordinates the channel of every access point. The controller tries to adjust each APs channel so that no two adjacent APs are on the same channel (reducing co-channel interference). If one AP has to change channels to avoid interference, then its surrounding APs also have to change channels to avoid co-channel interference. That in turn causes other APs to change, cascading the channel change throughout the network. You might end up reducing interference in one location, only to increase it somewhere else.