optimize for unknown for multiple quries

Hi every one
                       I had Problem in peroformance isuue.If i add OPTION(OPTIMIZE FOR UNKNOWN) at the bottom of the query, its increasing performance.But my question is   Really is it need to add this "OPTION(OPTIMIZE FOR UNKNOWN)" for all the quries??. I have lot of quries inside a single Procedure.So is it really required to add thio for all quries?? and all procedures??, Instead of adding this one to all the quries and all the procedures,IS there any option to add this in Database level or only one time for a procedure.??
Pls answer me.