The "genre" that always makes me cringe is when a critic or someone in the media refers to Pink Floyd as "space rock."
1) there is no such thing as space rock;
2) the only reason lazy-minded people call Pink Floyd space rock is because PF put out an album with the word "moon" in the title;
3) if these dolts would spend five minutes listening to virtually any Pink Floyd music, they would understand it has nothing to do with "space."
Give me a break.
The BBC broadcast of the Moon landings (long before DSOTM was released!) featured a panel of scientists on one side of the studio, and Pink Floyd improvising/jamming live on air on the other side of the room.
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I agree, there's no such thing as 'space rock', but I would argue that it can be a useful term for describing the sort of sound you're going after: lots of echo, lots of reverb, lots of tremolo. A very open sounds. Weirdly, I'd associate it with a lot of playing on the toms and cymbals, rather than hihat and snare. Very little in the way of groove or beat.
It's pretty much identical to psychadelic/trippy music. Early Pink Floyd, David Bowie, stuff like that.
As to the OP: The place I find 'genre' most useful is in Contemporary Christian Music (CCM). CCM is so homogenous, so much of the same sound, same melodies, same harmonies, same form (V1CV2CBBCC) and (above all) same chords, that everything sounds the same, very quickly. Especially since in a church service, the same musicians will be playing the same instruments on the same settings the whole way through.
Knowledge of genre then becomes VERY useful because you can break things up quite considerably. Slapping in one song (Funk), driving quarters in the next (classic rock), tone rolled off playing up near the fingerboard and not going above the 5th fret on any string (reggae)...same chord sequence for each song, TOTALLY different feel. And that's just the bassist's input. If the whole group is genre-savvy, it becomes much more effective, much more fun, and makes rehearsal a lot more interesting.
As well as playing technique, genre also has a big impact on rhythm. Reeeally worth knowing what beat is emphasised in each!
Peace,
SoundSupport