I didn't exactly understand - what was the benefit of using programming/python as opposed to programming, python? Was it that when the tag is registered then doing python from then on puts it automatically in programming?
It may be more practical tho. Currently as I see it, if you type 'python' it will offer you both tags and more i.e. 'programming/python' and 'animals/python' so you can choose quicker.
In many services you can actually use '/' in tags or something else such as '-'.
python ---Related--- python + animals python + programming
so that you could select python + programming to offer two tags at once.