Unselecting the eye icon of the alpha channel, in the channel window, result in hiding the RVB channels informations. So it is impossible to work or see the masked part of a RGBA.
When an alpha channel is present it's applied by default.
The hidden part let's appear a background checker-board unselecting the alpha channel should act as if no alpha was present and let people work on the RGB picture as if it was without zn alpha channel. This is what append on the other channels. Hidding the alpha channel result in hidding all the image (not many interest)