The histogram steps are used for SARGs only when a constant expression is compared against an indexed column and the value of the constant expression can be determined at query compile time. The following SARG examples show where histogram steps can be used:
where col_a = getdate()
where cust_id= 12345
where monthly_sales < 10000 / 12
where LastName like "Smith" + "%"
Some constant expressions cannot be evaluated ...