Filters are used when building a query to narrow down collisions from an entire set. If you have 100 collisions in the database and you do not add any filters, you will retrieve 100 collisions in the results. Some users may have the misconception that they will get 0 results without specifying filters and therefore select all the available filters. This is unnecessary and will result in an overly complicated query to see all collisions.
It is also important to note how multiple filters are used to build a query. If you had selected weekend days from the Day of the Week filter and then also selected Head-On and Rear End from the Collision type category the actual query would look like this:
Day of Week = (Saturday OR Sunday)
Collision Type = (Head-On OR Rear End)
Full query = (day_of_week='Saturday' OR day_of_week='Sunday') AND (collision_type='Head-On' OR collision_type='Rear End')
Within a filter the query language uses an OR statement, but when combining two or more filters an AND statement is used.