Well I wasn't really suggesting that the sub-plots didn't affect the MC or the main plot - just that they don't need to do so in a 'HERE I AM' style
Sibelius mentioned sitcoms and they are an excellent example of sub-plotting BUT in a very obvious and rather predictable fashion - pretty formulaic most of the time. Star TreK:TNG and the others of that era were great for this approach - a main theme (rescue people from a planet, deliver medicine, get lost, etc.) and a sub-plot (new recruit being trained, a love interest, someone getting stuck in the Holodeck). Normally these two elements did combine in the end - the new recruit proves crucial to solving the main problem, the love interest has to move away to appease diplomatic needs, the Holodeck provides the clues to getting home, etc. They were terribly obvious though.
I'd argue that
any sub-plotting that involves the characters does affect the main plot or perhaps how you read it without it necessarily having to be the 'missing link' that brings it all together at the end. Sure - it's great if your sub-plot can arrive at the finale with the reader going 'AHHHHH! THAT'S why he does that,' or 'THAT'S where it came from,' but I do think it'd be terribly hard to conceal that coming revelation from an astute reader. Once the cat's out of the bag it just seems (to me) a bit like a magic trick where you can see the wires.
I guess I'm just suggesting that sub-plots can be useful for other things apart from just being another pocket to carry part of the main plot.
Re-reading that, perhaps it's also a definition problem. I'm talking about 'sub-plots' as small stories told within the body of a larger work whereas some sub-plots are 'subroutines'
of the main work.
I dunno. However you do it, I think we can all agree they need to be there in some form - you can't just have a single story running from start to end.
J