I'm in the middle of writing an incredibly stupid report for school and it's annoying me, so I hope I haven't come across as rude anywhere. If I have, I apologize.
I was trying to understand how 'b' is a better direction of play than 'a', which I couldn't really understand. But taking what jts and Chew have said, I can see how you don't really want to force black to cap you at L5 unnecessarily.
If it was black's turn, I would probably split the top at J17. If I didn't feel like splitting the top, I would probably play L5 or P5 to profit from white's weak-looking group on the bottom (I'm not sure which is best TBH).
With white, another reason I chose 'b' is because I was thinking of it as a sort of inducing move into helping my two-space extension while maintaining good flow. Something like this:
- Click Here To Show Diagram Code
[go]$$Wc
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . O . . . . . . . . . . O . . . . |
$$ | . . . , . . . . . a . . . . . , X . . |
$$ | . . . . . . . . . . . . . . . O X . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . X , . . . . . , . . . . . , . . . |
$$ | . . . O . . . . . . . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . X O . . . . 1 4 . . . . . . . . . |
$$ | . . X O . . . . . . . . . . . . . . . |
$$ | . . . X O . . . X . 2 . . 3 . . X . . |
$$ | . . X , . . . . . , . . . . . , . . . |
$$ | . . . . O . . . X . O . . O . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]
(I didn't really read much further than this at the time, though looking at it now I'm losing my taste for it as white.)
But playing inducing moves and trying to have a flow to the game is something I'm rather new at, so I'm probably doing it wrong quite a bit of the time.