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PS. Over the years I've heard many togs say that using AF fine tune causes more issues than it solves and as a consequence never tune their lenses ...... were these people getting the best from their lenses ?? .........80% of mine needed tuning!

AF fine tuning as in AF micro adjustment? That is not the same as lens calibration.
AFMA is really only a bandaid to be able to overcome an AF issue in the field. 

AF on DSLRs can be "miss" due to different wave lengths not focussing on the same plane. It depends on what the AF sensor is sensitive to. "Recently (last few years)", I have seen many complaints regarding Nikon cameras and different AF results in daylight and in artificial light. I bet that is due to a certain band of "invisible" light (IR/UV) that the AF sensor sees in focus before it would see visible light in focus.
You can't AFMA that away.

And because the AF misses are due to different wavelengths focussing differently, and lenses do not have the same aberrations over the whole focus range and even less so over the whole zoom range, AFMA is even less helpful.