Sharp right-angle changes of direction in a foul drain are blockage factories. Solids decelerate at the bend, drop out of suspension, and build up until the run chokes. They also stop rods and camera crawlers passing, which makes both clearing and surveying much harder.
Good practice is to change direction using two 45° bends with a short straight between them, or a long-radius 135° bend, and to provide a rodding point at any direction change that cannot be swept.
If a drain in your property blocks repeatedly in exactly the same spot, a badly formed bend from a past extension or conversion is one of the first things a CCTV survey looks for.