Brake Discs - In reality what is the point of drilled discs?

I've recently picked up the 297mm discs + Cooper S Calipers from Philip - for which much thanks - and now intend to see if I can get them to fit under 15" wheels.  With the double drilled hubs (95.25 and 100) I would have the option of any 15" or 16" wheels.   
Far as I can see it, unless you live in the Alps or regularly to Track Days, a straight, undrilled Disc would be a better option.   After all every drilling or slot is less actual disc area.
It would be nice if it was possible to reduce their weight.  The hub, disc and caliper weigh in at 20Kg + 16" MX5 wheel / tyre (allegedly light weight) are another 16Kg.  Add the other bits and it's pushing 40Kg unsprung weight at the front. (Obviously a bit less for original 240mm + weedy metro calipers).
I cannot see how it could be improved by much. 

I genuinely believe for our use you don't need drilled or grooved discs.
The holes actually shave the pads a little. For road use they never get hot enough to need to desperately dissipate heat that quickly.
They do look good though.
Good luck with your new brake venture Vince...but don't forget to drive it summer is on the way!!

I've been trying to Guv.   Note the Sat Nav to Dunstable Downs. 

Home to -  https://www.londonglidingclub.co.uk/

Got there and it rained all day.   Back again June 9th (hopefully) 

I'm after a shot with the gliders in the background.

I did notice it but being up 'ere in the far reaches of our dear island it didn't register.
Gliding is fun..until you get further and further away from the airfield and lower and lower..and lower.
Never again! Lol..enjoy.

Drilled discs can crack around the drilled holes so unless your gonna be using them in competition and as such treat them as a disposable service item, then you don't need them!
Dimpled or slotted are better for road use, though still not really necessary!

If you have drilled discs slready stick with them as they can disapate a bit more heat but if you have solid discs they are fine. My current and last everyday cars have drilled discs so they are out there on mid range production stuff