In Canada we do this because it allows more representation in minority populations provinces. Very small provinces or Quebec get slightly overrepresented in seats. Rural areas have less people per riding but greater distances makes it logical to do that. If the person who represents you has to travel 100 miles by plane to meet up with small 500 people villiages compared to walking a few blocks in a big city to reach everyone. It doesn't make sense to make them ridings/counties equal.

On that same note the 500 person community will have different needs compared to other 500 person communities in the same riding. In a big city the issues will be very similiar citywide.