If you see gaps in where your pointing should be then it is time to consider having that particular section repointed. Repointing is essential to you house as it helps structurally but the mortar also protects against water ingress, preventing heat loss through the walls. When rain does come the water can freeze into the bricks and surrounding mortar thus expanding which eventually causes damage. If this is neglected it can lead to a damp and cold house.
Benefits of repointing
Repairs the structural integrity of your home.
Maintains and possibly can increase the value of your home.
Ensures weather guarding.
Reduces heat loss.