I ran into performance issues caused by parameter sniffing so many times using this type of construct

at work that I had to stop using it.

Now I use this:

declare @local_firstname nvarchar(50)

declare @local_lastname nvarchar(50)

select @local_firstname = isnull(@firstname,''), @local_lastname = isnull(@lastname,'')

SELECT ID, FirstName, LastName FROM People

WHERE

FirstName LIKE '%' + @local_firstname + '%'

and

LastName LIKE '%' + @local_lastname + '%'

It's more work up front but:

a) makes the query easier to understand (and therefore maintain) and

b) avoids slow queries caused by the use of inappropriate query plans via parameter sniffing

Just my 2c