**Performance:**

- Aggregates with GROUP BY generally faster for summaries

- Window functions preserve detail (more rows returned)

- Both can use indexes on partition/group columns

- Choose based on output needs, not just performance

Aggregates generally faster for pure summaries

Window functions return more rows (detail)

Both can use indexes on partition/group columns

Filter with WHERE before both operations

Choose based on requirements, not just performance

Using GROUP BY when detail rows needed

Using window functions when summary sufficient

Trying to mix GROUP BY and OVER in same SELECT

Not understanding output row count differences

Choosing based on familiarity instead of requirements