DTA Recommends to CREATE STATISTICS
statistics is used when query execution plan created. 


  Statistics for query optimization are objects that contain statistical information about the distribution of values in one or more columns of a table or indexed view. The query optimizer uses these statistics to estimate the cardinality, or number of rows, in the query result. These cardinality estimates enable the query optimizer to create a high-quality query plan. For example, the query optimizer could use cardinality estimates to choose the index seek operator instead of the more resource-intensive index scan operator, and in doing so improve query performance.


See http://msdn.microsoft.com/en-us/library/ms190397.aspx for more details.