Sorry, yes ADC means Analogue-to-Digital Converter (or Analog-to-Digital Converter, depending on where you learned English).
It's part of the electronics that sits behind the Arduino's 6 Analog inputs.
It wouldn't make things more than a few milliseconds worse (assuming I can extrapolate from what the spec does say). But it will lag, or not track the signal as closely as it could, which may cause problems.
Also, little voltage 'spikes' from noise might cause some angst. The lower the resistance the smaller the random effect (and in this case, random is bad
Think of a system like a radio with an aerial. If the resistance between the aerial and earth is big, you get a strong signal, if the aerial touches earth, the signal disappears or is reduced. A big resistance is like isolating the aerial from earth - the input to the ADC will be dancing with electromagnetic noise
. A low resistance will reduce the noise, a bit lke touching the aerial to earth, and the ADC will see the true signal that you are trying to measure.