Sacrificing leaf to promote flowers??

[orchidjunky]

Just out of curiosity...

I know for paphs its common to see the bottom leaf turn yellow if it's flowering.. but is this also the same for other orchids.. particularly oncidium/odonts?

I have an oncidium hybrid with 8 large flowers on two different spikes.... The plant itself has 5 pseudobulbs and has many leaves but one leaf at the center of all this mess is turning yellow... everything else on the plant is healthy... is this common???

Does the plant sacrifice a leaf for promotion of the flowers if there is not enough watering done.. or is this more of an overwatering issue as to why the leaf is yellowing but the rest remain green..