The optimum (in my opinion) is that leech telltales stream aft, but break forward now and again. That way your sail is generating maximum power and minimum drag.
If the leech telltales stream aft all the time, you are probably not taking max power out of your sail but still have the same amount of drag.
If the leech telltales break forward all the time, airflow separates from the leeward side too early and you are loosing power and pointing ability at the same time as you are generating lots of drag.
100% agree, and as Wouter says, trim on the mainsail is VERY critical sailing single handed. You must have enough tension in the leach to allow you to point (and be powered up) but not too much to stall.
Leach telltails are critical in telling you when this is happening.
