ISIS Level 2 routers under the same area
I have a question regarding to ISIS routing. As per my understanding, a level 2 ISIS router will have level 2 adjacency to level 2 routers. THe word level 2 adjacency as i knew is adjacency between IS in different area. My question is : Is it a common situation to have several level 2 ISIS routers under the same area ? What is the benefit and drawbacks to have this scenario ?