What is the use of additon in up to 1 rows in SELECT statement

Hi All,

What is the use of up to 1 rows in select statement.

for example

SELECT kostl

FROM pa0001

INTO y_lv_kostl UP TO 1 ROWS

WHERE pernr EQ pernr

AND endda GE sy-datum.

ENDSELECT.

I'm unable to get in wat situations we hav to add up to 1 rows

please help me out...

Thanks,

santosh.