Pull back and release every time. Forget that you even have the option of using the slide release button. This has been taught to me in the Police Academy. At my Department. By every department I know of. And in every SWAT class that I have ever attended. In fact if I was ever caught using the slide release button, I would probably be forced to do push ups, or at least be made fun of for days or months.
Why pull back and release? Because in a real gunfight you might have to manipulate the slide. Why? Reloading obviously. The slide locks back on an empty weapon.
Why is pulling back and releasing important? If done correctly using the hand over method, it doesn't require you to use fine motor skills. Fine motor skills don't usually work in a life threatening confrontation, due to the fact that the blood partially leaves your extremities and goes to your innards to help pump more blood, remember increased hart rate is another reaction to combat. The point is that you can't count on fine motor skills in combat, so train not to use them as best you can.
Why not use the slide release when loading the gun in a non combat environment? Because gunfighting is not something that you want to over complicate. You should always try and stream line your techniques. Or another way of saying it is, you fight like you have been trained. If you sometimes use the release button and some times don't, then you might very easily try and use it in a combat environment and that is not recommended.
I see no pros to using the release button. However I see a whole lot of cons.
The military taught me the same thing. Only use the release in extenuating circumstances.