utility of alpha value specified in glClearColor calls

the glClearColor function takes as an argument an RGBA value.

Is there any situation in which varying the alpha value specified will vary the background color observed?

or is the clear color specified as an RGBA quartet for congruity's sake?

[errno]

imagine that you use blending and your blend func is:
GL_ONE_MINUS_DST_ALPHA, GL_DST_ALPHA
and the DST_ALPHA is (for the polygons which doesn't cover other polygons) the value you just set using glClearColor(r,g,b,a).