Inefficient queries on partitioned tables
It depends on the query, so if you have a specific problem you'll need to give us details for the query (and possibly table structure) in order to get specific help.

Generally speaking though:


If the filter is not sargable then it is no help to the query planner in the same way as references to indexes where the clause is not sargable - for instance if a function or sub-squery that can not be simplified down to a single value for all possible rows is involved.
If there are other filters on columns covered by non-partitioned (or unaligned) indexes the query planner may consider searching that way to be more efficient than using the partitioning rule.