Does CAST(DateTime AS DATE) cause the entire table to be CAST before comparison? This is a very common need in the WHERE clause of our SQL statements:

 CAST(Something.CreationDate AS DATE) BETWEEN CAST(@firstDate AS DATE)
 AND CAST(@lastDate AS DATE)


All of the fields are of type DateTime that are cast to DATE. Does this cause a conversion to run across the entire table first and then comparisons happens or is this very similar to a scan on that table?
Whipped up a simple example on this using a handy calendar table. 

DECLARE @StartDate DATETIME = '2014-04-16 09:35:36.510'
DECLARE @EndDate DATETIME = '2014-05-16 09:35:36.510'


select
    *
from Calendar
where CAST(BaseDate AS date) &gt; CAST(@StartDate AS date)
    AND CAST(BaseDate AS date) &gt; CAST(@StartDate AS date)


When we look at the query plan for this we can see it's doing a simple index seek and all is well.