add comment to justify random reduce function's existence
add comment to justify random reduce function's existence

dimagi/commcare-hq,dimagi/commcare-hq,puttarajubr/commcare-hq,SEL-Columbia/commcare-hq,SEL-Columbia/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,qedsoftware/commcare-hq,dimagi/commcare-hq,qedsoftware/commcare-hq,puttarajubr/commcare-hq,dimagi/commcare-hq,SEL-Columbia/commcare-hq