At high RPM and wide open throttle, there is no significant differences between either one. Here a single throttle body might have a slight advantage since you have less turbulence in the intake runners caused from throttle plates and stuff.
The biggest, most noticeable advantage you will feel from using ITBs is when you are driving on low throttle or idle with something like a max effort high RPM camshaft that has tons of overlap. The ITB throttle plate will help prevent the intake charge from being contaminated with exhaust, making the engine run smoother, and the race cams will sound less like its going to die at idle.
For a single throttle body and a crazy cam, the intake plenum will be under vacuum under low throttle openings. Then when your intake valves open, the exhaust will sometimes flow backwards into your intake plenum, causing the engine to run rough from messing with the air fuel mix.
With ITBs and a crazy cam, even at low throttle openings your forced induction intake plenum will be at a higher pressure than the exhaust, then no exhaust will flow out of the throttled intake runner to contaminate the intake charge of another cylinder.
So basically ITBs are only really needed if you need to drive around on the street with a camshaft spec that is not normally streetable.
There are other minor stuff you can do with ITBs like using it to tune the direction of air flow into the cylinders, and improve throttle response like already mentioned, but the race cam low throttle performance improvement is going to be the biggest advantage. And the more extreme your camshaft, the bigger the advantage.