I have seen tutorials where it is explained that if you select multiple objects and want to have the same values in certain fields you could either press Alt+Enter or hold Alt while you click in the field to type in the value.
This is simply not correct. In your first example and last example, the cubes and the sound strips, there is a difference between using Alt+left-click before typing a value or using Alt+Enter after typing a value:
Alt+Enter applies the same difference to all values as the one between the original value you are changing and the new value, so it works relative to the original values.
Alt+left-click and then typing a value is putting the same new value in all fields, it is working absolute on the values.
On the mesh vertices in your second example it's not working the one way or other because above the location values it clearly says Median:, which means this is always the median value of all selected vertices. Changing the median will only move them all staying relatively the same to each other, and only scaling them to 0 on one axis aligns them on this axis.
Of course, most times the tutorials get the correct result because often the objects they want to change have the same values, so changing them with Alt+Enter will result in having them all the same new values as well. The differing results in both methods only appear if you change objects with different values.