Acid-Base Titration, why does for a weak acid indicator, [HA] = [A-]
In an Acid titration, we want the end-point to be as close to the equivalence point as possible. 

Different indicators have different end-points (they will change colour at different pH values). 

When an end-point is reached, the colour of the indicator will change with respect to the [$H^+$] concentration of the solution it is measuring. 

As [$H^+$] increases, there will be a point when [HA] = [$A^-$] and depending on the indicator used by the person doing the titration, this would be close to the calculated equivalence-point. 

Note, the difference in volume between the end-point and equivalence-point is very very small, hence we can approximate the end-point as the same as the equivalence-point in any experiment.