Seizing shrouds to spreaders

[Ryan]

Looking through the archives Brion mentions that you seize the shrouds to the spreader for vertical and lateral security. In regards to vertical security, it seems that you need to tension the shrouds before you lash then to the spreader tips so that subsequent tightening of the turnbuckles don't actual pull the spreader tips down. Is this the case or am I over thinking (again!) this?