Benefits from less "rotating mass", lighter weight wheels & tires
better eff. brakes & better acceleration, better handling {in most cases}
less wear & tear on parts etc.
Downside is potholes will feel more severe, road noise will increase
& a tad bit of ride quality will go away with lightweight wheels...
Skinnie's up front will give/have less resistance to the ground
but in a heavy car it won't be very noticeable,
but better weight bias front to rear for a standing start accel. test
more air in a "slightly" wider tire {like a 60 series vs a 5" wide skinny}
at about the same basic weight/height rollout,
will do about the same thing "basically", nominal differences,
but if you drag racing
it doesn't hurt to take advantage of every thing you can,
to get a heavy car moving & a better weight transfer
{weight bias} especially off the line, more will be made up in 60' times
& 330', the even 660' times, to help improve the heavy cars performance,
the rest depends mostly on your engine & HP
& a ton more $$$'s spent to achieve, significant gains...
{mainly for mph, The right converter, gears & shocks, good weight
transfer will do far more, but lighter rims certainly help the total combo}
Less rotating mass "anywhere", be-it tires, wheels, crankshaft, rods,
driveshaft, axles, drums/rotors etc.
Is usually always a good "rule of thumb", in any type of performance build...
"weight is weight, no matter were, reduction is a benefit & it all adds up to"
Heavier the car,
the less noticeable the effects of lighter weight wheels will effectively be...
A really lightweight car you'd notice a 40#-100# weight reduction...
Here's an old Hot Rod article but still holds true...
Quick read, it's a "Real world test", mainly straight line acceleration...
{Even if it was a Heavy Cheby}
an increase of 1.12 MPH & 0.111 sec. faster 1/4 mile
with 82+#'s less rotating mass {wheels & tires},
in a big block 12 second 3500# car {wild *** appr. guess ?}
steel Ralley's (189+#'s total)
vs Centerline Alum. wheels (107+# 's total)
http://www.hotrod.com/articles/light-vs-heavy-wheels-comparison/