That a cloud of ashes from an Icelandic volcano can cause air traffic in most of Europe to shut down is a nice reminder that redundancy can be useful and valuable when the unexpected happens. Where rail lines and ferries can take up the slack, most travelers are inconvenienced but not stuck, but wherever airplanes have a monopoly, tough luck. The present bootleneck is costly to the air carriers and big trouble not only for passengers but for the increasing share of post and freight that is flown. The time advantage of jet travel is real, but shouldn't there be more travel alternatives available? Fast and affordable passenger ships, for sure, and isn't this a good argument for a more thorough revival of dirigible airships as a more gentle mode of air travel?
Here's the reminder: a bit of redundancy in musical performance practice is also useful. Conducting cues, for example, can often avert difficulties or rescue a performance when caution was insufficient. Doublings and cued notes in parts are useful. Players are wise to bring extra reeds, strings, bows, mallets, etc., the spare tires of concert life. When electronics are in play, redundant power sources, mikes, cables, amps, speakers, recordings, computers and software can save a concert. And in the composition itself, repetitions and doublings can serve multiple purposes, both aesthetic and a practical.