I've always done it, I think it's because before I played guitar I played violin, and because of the alternate bowing's only picking down made no sense to me.
Of course, now I have trouble just doing down picks

If one is going to call themselves a guitarist, let alone a musician, alternate picking is as basic and essential as knowing the notes on the fretboard. YMMV.

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You dig?

I use it but it seems to be when I am most likely to drop my pick.

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You're only as strong as
the drinks you pour,
the tables you dance on,
and the friends you roll with.

It's something I do without thinking about it. For speed work, it's essential and I'm probably doing it all the time anyway. So there.

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alternate picking equals fluidity and speed. trying rattling off some clapton with all downstrokes

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Keep rockin'