While tell tales will let you know how to trim your sail for peak performance, ignoring them for the sake of comfort may also be wise. Having poorly trimmed sails will cost you some speed, but the peace and tranquility it brings could be worth it to you.
When sailing downwind in light winds, the main steals a lot of air from the headsails. If you have the sheets on the headsails eased, these sails will lift with wind and then slat as you come down a swell. When the sail falls, so does the tension on the sheet. The sheet block will then fall onto the deck and make quite a bit of noise.
Being how the wave period in the Atlantic is around 8 seconds, this means that every 8 seconds you will hear a "TWANG!" on the deck. Do this for an entire day and you might go crazy!
In situations like this, you are faced with two options:
- Either drop the headsail so it stops slating.
- Over tighten the sheet to avoid it from going limp.
When you drop the sail, you lose all of that sail area entirely and unbalance your sail plan. This is far from ideal, especially on a broad reach, where you need the headsails to provide lee helm.
Over tightening the sheets will keep the noise from happening, but it will make your sails less efficient. This might cost you a fraction of a knot in light airs.
If you are deaf, or willing to put up with the noise for the small amount of speed gained, then by all means, trim based on the tell tales. If you prefer peace and comfort, then it would behoove you to over tighten the sheets and keep the peace inside the cabin.