This is actually a very good question, @Drfosters, and it has really made me think.
For me, choosing to go by the shortened version of my name was symbolic of a big change I made in my life at that time - I gave up nursing, where I was unhappy, and went to university. I can remember thinking on day 1 that this was a new chapter, and so I would mark it with a new, everyday, name.
My life was a lot happier after I'd given up nursing than it ever had been before, and I guess that influences how I feel about the shortened name - it epitomises the new happiness I felt.
But both my parents were still alive at that point, and I did not want to hurt them by rejecting the name they had given me - plus, if I am honest, I was still afraid of my mum, and didn't want to face the huge fall-out there would have been, if I had officially changed my name. Mum was a very forceful personality, and she had never respected me as a person - I had never been able to express my feelings to her because she would simply refuse to acknowledge any validity in what I was saying - and her reaction, when I finally did pluck up the courage to ask her to use the shortened version, was not positive. Basically she refused, point blank, and didn't change her mind about it for years - and even when she did start using the shortened version I had chosen, she made a big song and dance about how difficult it was for her.
She only died a couple of years ago (dad died back in 2000), and there is no way I could have legally changed my name while she was still alive - and now almost everyone knows me by the name I have chosen, so it doesn't seem worth the effort.