What's the best way to account for saw blade width (kerf) when cutting boards?
Yes, you might want the highest precision possible - for example when you build furniture which benefits greatly from precise cuts. The most convenient way would be to draw the line that will signify the edge of the piece you want cut so that the blade cuts the line and whatever material is on the far side of the raw board. Something like this:

 |the detail you want|line|remaining material|
 |                   |blade cuts here|


This is quite easily achieved with power saws even without a guide and will be more of a challenge with hand saws.