The effect of extending ground to any area on the board - not just the edges - is dependent on your circuit design requirements.
It's generally not a good idea to extend copper all the way to a board edge, as it will create exposed copper on the edges of inner layers, delamination, foil separation - a host of issues. The minimum amount you need to pull back from the edges is based on your fabricator's abilities. And don't forget the material removed by the angle of the v-groove when calculating this.