Fitting a total energy (TE) probe stops the vario being affected by pilot induced speed changes. This makes it much easier to differentiate between a "stick thermal" and a real bubble or rising air.
With a Total Energy probe (TEK) fitted the variometer senses the vertical movement of the airmass, rather than the vertical movement of the model. The TEK does this by sensing the model’s speed, and adjusting the pressure into the variometer appropriately. With a perfect TEK you could dive a model and loop it, and the vario’s tone wouldn’t change - as long as you didn’t fly into lift or sink. Conversely, you could trim a model to high speed to escape an area of sink, and the TEK-fitted vario would continue to sense the vertical speed of the airmass only, without being confused by the higher than normal sink rate of the speeding model. Thus as soon as you had escaped the sink the vario would return to the normal tone - without the TEK you would have to slow the model up before you could rely on the vario’s signal.