I have played at racing
and seen backstays
Racing answer depends on conditions at time. Cruising answer when watch your boat and mast
Racing some of the signs of to much back stay tension I have seen:
1. Door to owners cabin
aft not opening when hull
2. You cannot pull any harder on the adjustment system.
3. The mast
starts taking funny
4. The seams on the wooden planks start opening up due to stresses.
fittings starting to weep due to over loading.
With my boat I would not play those games.
Just remember depending on the design of the rig one wire effects another...
Adjusting the back stay (depending on the amount) you can:
A) bend the mast, changing the set of the main sail.
b) tension /slack your lower shrouds?
C) Increase fore stay tension (the plan?),
D) change the rake of the mast, may change the "feel" of the boat. To do this significantly you probably have to adjust the forestay (also worth considering?)
Remember some forestay sag should be cut into the sail. Sail makers know forestays sag.
Lots of tension on the main sheet can increase forestay tension.
Cruising what do I look for?
A moderate forestay tension.
A mast with a slight aft bend or straight depending on mast type.
Not to much slack in the rigging
so the mast does not slop around in a sea way.
A moderate back stay tension,(I often climb onboard over the stern using the back stay as a support).
Do not just look at it in port, sight up the track in varying conditions and headings beating, reaching, running etc, it can change significantly.
All masts are designed to bend and move. When ever you are on another boat feel there rigging
I am sure some one will disagree with some of the above.
If the stick stays up and she is sailing ok, you have not got it far wrong!