provides the data to the CDI unit for the third part of the 3 Dimensional ignition mapping. This works along the same lines as a car distributor with a vacuum advance on it. Lower throttle openings will tolerate, and sometimes need, more ignition advance than heavy or full throttle does, so having that information allows the CDI to map
the timing based on both engine rpm AND throttle opening. When the TPS
either fails, or is disconnected, the CDI substitutes a full throttle value for the missing data and maps the timing based only on the engine speed. What may actually suffer most, if anything noticeably does, is part throttle, high speed cruising, fuel economy, etc., rather than full throttle performance, since the unit is working on the assumption that the engine is always at full throttle.
The two threads linked tell more.