Is there is any Performance issue while using ISNULL() in SQL Server?

Question

I am using ISNULL in MS SQl server 2008, since my table is too huge, whether using of ISNULL may cause any thing to the performance ?.

Than

Answer 1

Watch out if using ISNULL with a sub query as the replacement_value.

Seems like it runs the sub query even if the check_expression value is not NULL which doesn't help performance.

CASE performs as expected.