Comment by skeeter2020

compression is a side effect but not really the goal. To simplify, analytical queries often filter on a specific column value, and if these are laid out contiguously it makes disk-level reads much faster than rows that would involve read-skip-read-etc. In transactional systems data is typically written as rows though, so that's likely slower in a columnar system. As a general rule, heavy read workflows with known access patterns is going to benefit from a columnar layout.