in reply to why avoid & on function call
"What is the difference between including one and not including one?"
The difference is that people who are more experienced can tell that you're learning from a book published in 1998 when you're using it out of a legitimate context in 2020 ;)
In all seriousness, this is a good, valid question, because I still see new questions pop up from time-to-time on various sites who use this technique. It's usually combined with a lack of strict and declaring/defining variables without my.
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