Your question is also a f() of the resolution and accuracy you are
looking for. Clearly digital ground will have noise on it, and ohmic
drop. Noise you can take out of A/D result by filter/averaging. However
it has to be uncorrelated noise to be effective. And digital noise has
strong correlated components in it typically. Ohmic drop by cal routine.
And all of this a f() of resolution you are seeking.
Possible references that may be of use -