slack in safety chains

I know this issue has been beat to death, and I don't really want to start another pie fight, but it's pretty much proven you can effectively control the trailer even if it's sitting on the safety chains, so having the brakes lock for that situation doesn't make sense to me, especially if you can otherwise pull off the highway safely. I think if it breaks away completely, then you'd want full braking ASAP. Hence the term, "breakaway switch".

As to the safety chains, you don't ususally need a lot of slack. Probably much less than most people have. There isn't a lot of difference in length added or subtracted by turning and compound angles. Definitely don't have them dragging on the road like so many seem to. Have someone stand and check the slack while you go through full turns.

What downtheroad said, PLUS; some state laws require that the safety chains be crossed under the trailer tongue. That is, the left chain must be connected to the right attach point on the towing vehicle, and the right chain must be attached to the left attach point.
There has been an ongoing discussion about the length of the breakaway cable. Some say it should be short enough to lock the brakes whenever the trailer comes off the hitch, others say it should be long enough that it will lock the brakes only if the trailer breaks completely away from the towing vehicle.
Since I am not sure the safety chains will be strong enough to withstand the shock of the trailer coming to a sudden stop, I tend to agree with the "long enough" group.

Long enough so they don't bind when turning or backing.
Short enough so the tongue won't drag on the road of it is disconnected from the hitch.

Also have to consider the length of the brake-away cable in the equation.