When you load an existing image in Photoshop or Gimp, it is a single layer with no alpha channel. One reason why someone would need to add an alpha channel to that layer is if they want to cut away parts of the image and have a transparency underneath, rather than a white layer. Besides this (having a transparency layer to fall back on) What other reasons is there to add an alpha channel?
Is it actually best practice to always add an alpha channel to each newly created layer when editing a photo or image?
And technically, what really happens behind the scenes when one adds an alpha channel? Is the alpha channel actually a new layer, but not displayed as a new layer in the console, that adds additional space to the image file equal to that of its parent layer? What else is going on