A note on single joint accessory movements.
More often than not the purpose of a single joint accessory movement is to train said joint through a much larger range of motion (ROM) than it is exposed to in a larger, compound movement.
Consider the triceps involvement in a bench press; safe to say they are pretty important. However the elbow joint itself isn't taken through a massive ROM due to the bar meeting the chest. Thus we train the triceps (elbow joint) through fuller ranges via things like cable extensions, DB Skull crushers etc.
Should you find yourself maybe feeling these movements in areas like the traps or delts, we would argue that you are perhaps sacrificing range for load. In which case we would encourage you to pull back on the load and focus on "feeling" your way through the movement.
An analogy we use with a lot is - "the barbell is our sword, but the accessories are our armor. Sure if you have a really sharp sword you may take a few people down in battle, but without armor; you're probably dying pretty quick." We build this "armor" via accessory movements like tricep extensions, so take these movements through full ranges and build the best armor you can.
Let's build armor together: