Why pre-shave oil?

I see that there are many folks here who advocate the use
of pre-shave oil. I can understand how and why that might
be useful prior to shaving with an electric razor, but oil
on the face before wet shaving? I don't get it.

I gather that the arguments in favor of pre-shave oil are:
1) it conditions the skin; 2) it increases razor glide; and
3) it softens the beard.

I can understand (1) it conditions the skin...relieving
dryness, restoring suppleness, protecting the surface.

As for (2), it increases razor glide, that sounds counter-
productive to me. After an oil application, the razor
may glide over the skin, but wouldn't the razor also
tend to glide over the whiskers as well, thus reducing
the closeness of the shave?

Finally (3), it softens the beard. OK, so hair will absorb
oil, thus softening it. However, as I understand it, in
order to get a proper shave, the whiskers must first
absorb moisture. Now, oil repels water, and I thought
the object of using shaving soap was to remove oil from
the whiskers, thus allowing water to be absorbed.

So why apply oil and then immediately try to remove
it? It would seem to me that the appropriate time to
apply oil to the facial skin would be AFTER a shave, in
order to offset the drying effect of soap and the irritation
caused by the razor.

Maybe my logic is faulty. Please enlighten me.

Thanks,
Paul