I heard on one of the old Jamil shows that pitching actively-fermenting starter is a good way to get noticeable but subtle yeast character in a beer. You need to start with an adequate amount of yeast, but basically to 'get the yeast going' before pitching it. He was referring specifically to saisons, where you want a good amount, but (IMO) still subtle ester and phenol production, and a complete fermentation. He was saying it was better to do this as opposed to purposely underpitching or fermenting hot, both of which are risky to say the least.
We ended up trying this on two IPA's with Conan yeast (from which we wanted ester production) and the results were awesome. 78 and 82% attenuation with the esters we wanted.
My question is does anyone know the science behind this method, assuming, as stated, equivalent pitch rates? Why it creates SOME yeast 'character', but not too much? The yeast are already in the growth phase, and I guess it would maybe minimize lag phase?