This is about "balance". It takes a balanced baitcasting combo to cast very light weights. Well, actually, it doesn't. You can do it with heavier gear if you're willing to put in a lot of practice time, but I'm guessing that wasn't what the original poster was asking about.
I use Daiwa Alphas reels for the lightest of weights. .
I have Daiwa Zillions which never see really light weight baits, so I don't know if they're capable or not. I have no reason to find out. The Zillions are spooled with heavier line than the Alphas and are mounted on much more powerful rods. This makes them unsuited for casting the lightest of baits. If they were all I had, I would have to make do, but I have better options.
I have Fuegos, which are good down to about 1/8oz, but given the line and rods utilized, these combos are mostly used with baits in the 3/16 - 3/8oz range. Again, if they were all I had, I could use them for the lightest of baits.
My Alphas are spooled with light line; one with 6, one with 8 and two with 10lb test, all mono. The best combos I have for light weights are as follows.
Best: Alphas 103, 6lb line, St Croix LTB 6'9" ML-XF. Good down to 1/16oz never tried anything less
2nd Best: Alphas 103F, 8lb line, Kislter Helium 7' ML-MF. Again, good down to 1/16oz
The other two Alphas are mounted on medium power rods, so they never see really light weights, but they both will cast 1/4oz just fine.
I made the decision a couple of years ago to get re-aquainted with spinning tackle, so I pretty much use that now when I need to go under 1/8oz.
I would love to have a Pixy SPR, but the cost of admission is too high for me.