Well, now that's a great question!
Down strokes and up strokes are tools to be used. You can create some *great* sounds with upstrokes. You can really color your chords with upstrokes. You can make a lot of people believe you're doing some awesome guitar work by using upstrokes in strategic places.
A lot depends on the sound you want or the type of rhythm you're trying to create.
Here are some
samples ......
Be sure to listen to it all. It's only about 2.5 minutes. There is a Neil Young and a Bob Dylan sample in there.
It's not the best of lessons but may will help out.
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Les