There are so many reasons you need a crocheted detachable collar that I was hard-pressed to fit them all into this story. The best reason I could think of was the next time you feel compelled to attend a neighbourhood meeting about the Unitary Plan, you can cool down by simply unbuttoning your detachable collar and stuffing it discretely in your bag or pocket.
The history on detachable collars is sketchy but they were a largely practical invention designed to be easily washed in a time before electric washing machines and they still seemed a given right up until relatively recent times. My mother recalls a detachable, highly starched collar on her nursing uniform in the mid-60s.
They allowed for shirts and dresses to go an extra round before they hit the washing tub, and they allowed for a little reinvention: who needs a new frock or sweater when you can just change the collar? I could get into them in a big way, which is just as well because I made three of them in next to no time at all.
Don't be put off by the perceived complexity; if you know the crochet basics you'll be well placed to make your own collection, one for every day of the week, and they look quite fetching, too.