While blindness and poly other and holds will rise up as the ohhh and ahhh...
use spells which avoid the downside...
Single most potent spell to be chained...
Greater Magic Weapon (imagine 12th level sor who throws a sixth level chain GMW and enhances 13 weapons/ammo-sets to +4 for 12 hours!!! Thats one sword, one bow and 50 arrows EACH for every member in a four man gang.)
Haste is also good, why waste time with mass haste.
Dispel magic (targetted version) is wonderful as you get rolls vs all the spells on the chainer victims... not that dispel rolls are not saves. Hit their mage and also drop nearly every potion liquored fighter's buffing at once.
etc etc etc... chain is IMO more effective at spells for whom save is not an issue, like all the above. its use for offense is hit and miss, due to the save thingy, although you will typically get one extra failed save.