MSSQL Conditional where statement

Conditionally placed where statement (in stored procedure)

WHERE BLABLA = BLABLA
-- here it is  AND clause will only happen when @FN is something
AND 1=CASE WHEN @FN='' THEN 1 ELSE 
	CASE WHEN @FN = CL.SUBTITLE THEN 1 ELSE 0 
	END 
END

Another example:

...
 
WHERE
	 E.CGE_PATHLENGTH=2
	AND 1=CASE 
		WHEN @TOPLEVELCODE <>9 AND  E.CGE_START=@TOPLEVELID  THEN 1 
		WHEN @TOPLEVELCODE =9 THEN 1 
		ELSE 0 
	END 
.....