Ask about unused indexes

 Hi all,

      My database version 10g (64 bit). OS is linux 64 bit

      I want drop unused indexes on tablespace. But at first, I must monitor all of indexes. I read some documents about monitoring indexes with MONITORING and NOMONITORING. I use:

        select 'alter index '||owner||'.'||index_name||' monitoring usage;'
        from dba_indexes
        where owner not in ('SYS','SYSTEM');

    ---> Monitor all of indexes from my database server exclude SYS and SYSTEM. But how impact of this work on perfomance of database ? My database is slower ? or size of tablespace that contain this indexes will increase ?

    Plz, can help me about it ! Thanks