whoever told you that is out of his mind,
the tech2 will show you two readings of fuel trims one is called block learn and one is called integrator. In classic terms they are
block learn = long term fuel trim
integrator = short term fuel trim.
the long term's job is to keep the short term near to zero. but a long term too high (more than 15%) means the engine is seeing less fuel due to either starvation or air leak or bad measuring equipment. In such case the engine will balk on acceleration.