The average brick home was built in the late 70s. As solid and durable as brick and mortar are, over time it will break down. Take a walk around your house and look for large cracks in the mortar or even worse, cracks that run right through the bricks themselves. These cracks will grow over time causing the brick to fall out and will let in water, bugs and more.
If you have a brick chimney, they are very exposed to the exterior elements and probably from the heat from the inside. When the bricks on a chimney start to fail, you need to have it addressed as soon as possible. A good brick mason will diagnose the issue and when the bricks are replaced, they will go down a few feet below the damaged brick and replace them as well.
Ever hear of tuckpointing? It is a term that is common in the masonry field for the repair of damaged mortar joints without having to replace and rebuild the brick. Brick is designed to last longer than the mortar. So if a professional mason recommends that you need tuckpointing, they are suggesting a process to remove the existing damaged mortar, fill in with new mortar, then filling in with a color that most closely matches the mortar on the rest of the chimney, house or porch. Masonry is a true art that should always be performed by a licensed brick mason.