I agree with Benzebub. I also find the cross mod useful. I mentioned elsewhere in this form about that trait of the OB6, that there are some subtle, as well as not so subtle features of the instrument to allow modulation of sound. Cross Mod is one such feature that I like a lot. Having cross mod feature to modulate sound is perhaps not as familiar outside of the modular realm, but one that gives character to this instrument.
While I never craved on-board effects, I learned to like the availability of such on the OB6. I'm sure some synth purists might argue, but effects IMO are simply more available ways to modulate sound. The effect I find most interesting on the OB6 is the ring mod. I'm not clear if this effect is truly ringing both oscillators together in traditional terms, or whether this is just some digital replication of that being applied. Nevertheless, the end result seems true to form with various ring modulators I've used. Combined with the various filter settings some great formant type sounds become available.