My son has an unusual middle name, which he does not use in general , and strangers would be very unlikely to even guess it. He travels a lot , lives on his phone of course, but we have a good use for it. If I ever get a text purporting to be from him, saying he has lost his phone or any other of the scamming things, lost his wallet etc etc, I simply reply "whats your name?" and if it is him he knows to put the unusual name. As the texts appear to be plausible, given his travelling, it is a useful check. Within our family we also have an unusual name that came from a grandparents family, and we also use that in the same way. It is not on any passports or documents , and we are careful to keep it to ourselves.
I actually have two middle names and my sister and brother have one each. Handy for using initials on letters etc. Despite whatever care you take naming a child, over the years things change. My brother was christened Terry as my parents liked a simple name, definitely not Terrence, and thought there was nothing it was likely to be shortened to. Wrong! He was called Tez, Tez Ray , Top Cat by friends .
Apart from family names you seem to find names come and go in fashion , but I wonder if any of you have a sense of colour that belongs to specific names? For many years I did not like the name Maureen and a dark purple colour was somehow connected to the name. Then when I lived in Portugal I met another lady called Maureen , who has been a lifelong friend and whilst I still seem to see a colour it is more a pale pleasant violet colour.
The only thing I tend to mention , even these days, is to think twice about giving girls a second name beginning with a vowel, as if in later years they choose to marry or change their surname you can end up with some unfortunate initial combinations, as a friend , who became Shelagh Olive Downes found!
One good thing about second names, is that it helps if trying to look up a family tree , especially if you have a common surname.