slapd read-only slave replica

Hello,

Does it make any sens to enable indexing of any attribute on read-only 
slave syncrepl replica? I mean, isn't it just waste of resources, or, 
actually, is not a waste a resources at all, since replica is read-only 
and does not write anything anyway? This, I think, apply to any version of 
openldap.

Regards,
DT