Ceramic bearings provide essentially no benefit by themselves, but the aggressiveness of the seals and the type and fill of grease in a bearing can make a big difference.
That is exactly what I've always said on this forum: don't go for ceramic hybrids just to gain some Watts. The ones you can buy are more often than not just standard industrial bearings and those (together with regularr steel ones as well anyhow) are really not designed for our puprpose, i.e. low speed, low rev.
There are however other advantages to ceramic bearings which do allow them to be used with far less viscous lubrification and non-contacting seals.
For that to be possible and last for at least as long as a typical steel bearing you'll need to find the right lubricant (oil or grease) and, more importantly, a well made ceramic hybrid bearing.
They are out there and no, they do not have to cost an arm and a leg to be of fine quality either.
Only then there will be a small wattage saving but more importantly (to me at least) they will run more consistently throughout their useful life provided they're being serviced accordingly. (see the appropriate Bell curves)
Seals can be broken in prior to mounting them in a bike which is what's been done by several Pro team mechanics whenever deemed beneficial.
Grease is run in as it is pushed aside which is one reason to use bearings with only a say 60% percent pack rate (unless there is no seal at one end of it). As Frieke says, smaller balls cut through it more easily as well.
Last but not least, go for bearing with phenolic retainers or better. Steel retainers in ceramic bearings are out.
Oh, and if you must use ceramics with contacting seals then you'd better use grease as well. If not the seals will run dry which will increase friction dramatically.
P.S. Current Campa CULT bearings are essentially grooved ball bearings with adjustable preload, not true cup and cone bearings. Seals can be set up so they're non-contacting (only for the more patient among us) or, if you're willing to maintain the bearings regularly, you can run them "al fresco" which is very straightforward without the seals present.
I've done some checking for wear on the Cronitect treated cones and have found none whatsoever even after 30.000km on just a few drops of Triflow.