What's the gain here? Is coil on plug that much better?

Its like sharing a girl with seven other guys... Its better to have her all to yourself....

Ok. I'm building an engine on paper and am wondering if that's something to consider.

Better? yes... Necessary? No... How much do you wanna spend? I would put my money on other upgrades..ie. rods, crank, heads, lifters, valves, push rods, springs........................................... ......

Hmmm, I see.

If you want to go crazy you can always put a mag on it...

After all your other pieces are in place and you want totally stable timing control ,then consider crank triggered distributer-less ignition. I agree with Bawana on priorities

I.think.the 496 gets it because it already has it .hall effect distributor guys have gone for the last bit of hp.by manipulating the trigger tin in the distributor to tailor spark event for each cylinder .
So what do you get the engine for Christmas,that already has everything ?
Coil on plug ignition system .

Save your money unless you're starting with it on the engine

depends on what you are trying to do....if you are running a "basic" ignition and a carb no, but if you are doing a MSD style and EFI I would say yes, the RF interferance that is flying around with the MSD box and some aftermarker EFI ECM's can drive you crazy, so at that point the LS coil packs, crank trigger, cam sensor deal is far better...Alex Haxby/Eddie Young can answer the fine points on this...