I always assumed that the focus changes as you zoom in. Turns out there are parfocal lenses that don’t, or at least minimally.
If you think that is due to cheap lenses you should weave that into your advice that you give. For me it doesn’t matter because I simply don’t do it. 
George
Thinking it over there are some practical issues. It demands that you use a tripod and that the subject is static.
George
Since there is no way to decide which of the many AF spots are actually going to be sharp, I use “back button assisted manual focus”, so I can determine the depth of field as well as the point of sharp focus.
You also need to reduce the focus points to one single point in the middle.
No to the first but the second can be helpful.
The photo looks a little bit soft for this good lens. Maybe it’s due to diffraction – f/10 on APS-C was used, but I would expect a milder effect (not sure, though). So maybe it’s due to image stabilisation mishap? IBIS or VR can sometimes give blurry results when you press the shutter while it’s still trying to get stable. Just guessing.
Here’s is my quick try in “auto mode” 
, with VC-2 added to @Joanna dop, requires FilmPack license. What do you dislike?
D6700685.ARW.dop (73.2 KB)
I tried to get the main subject more visible, hence the crop and highlights corrections. For that purpose I had to sacrifice the pool geometry, which was partial anyway. Slightly corrected moire, seen near the ‘FUMARE VETATO’ sign, but couldn’t use 100% due to some artifacts introduced by the tool. Perhaps WB and some LA corrections should be added, but it was a quick try to show some fine contrast points.
If you want a series of images with the same focus, the half-press configuration wont’work. Keeping the same focus is useful for panoramas and for multi-shot HDR processing
It works on my cameras. Metering can also be locked in this way.
When taking a series of photos, if you completely release the button, focus and exposure lock will be lost. For example, in HDR bracketing, if you have to adjust the exposure between shots and you use the half-press for focus lock, modifying the settings becomes very difficult if you have to keep the release button half-pressed.
Which is why everything has to be manual
Well no, that’s my point. I can select which of the AF points I want to have active. In practical terms, if I want focus to be on the bottom left hand corner of the sensor area (in truth, just inside, but at the southwesternmost AF capable point) I can set that up before I half press the shutter. Knowing that the AF point is where I want it, I only have to press the shutter. Oh, I forgot to say Sony allows you to tell the camera not to fire unless the lens is focused.
I had no experience of AF cameras before I got into Sony. My first Sony body only had 15 AF points, all contrast detect, and at that time BBF might have been a useful adjunct to my toolset. But along came the A77ii with 79 AF points, almost before I started worrying about where I was focusing. And the rest is history.
We all have different histories as photographers, whether we are professionals like you or amateurs like me. If we didn’t it’s likely we would have much less diverse styles, both in how and what we capture and in how we then process it.
Provided you have enough fingers
Using AF only with the AF-ON button is very useful in some cases and useless in other. If you shoot fast, unpredictable action, you often have to use the thumb for the joystick and then there’s no thumb2 for AF-ON button. Having shutter release already half pressed makes the press faster, which may be critical for capturing the right moment. This all depends on particular subject and camera capabilities.
Let’s assume you are shooting a static subject. There is no need to have more than the one AF point in the centre of the frame. You point that at the subject you want to be sharp and press the back button to set the focus and not touch it again. The focus is now set and will not change, even with reframing or half pressing the shutter, because the shutter focusing has been disabled. This is the benefit of back button focusing. It is so simple and fast. In this case, the button is not intended to hold to maintain focus, it is there to “set and forget” focus, allowing you to concentrate on measuring the exposure and setting ISO, speed and aperture.
I think it’s common to use a single AF point.
In other words. Back button pressed activates the AF, releasing the back button locks the focus.
George
