Depends on the situation as to whether it's detrimental. Proxy-aggregation, as this is called, can alter traffic patterns in dual-homed situations. The change is not always bad, though it is often un-desirable.
In general, proxy-aggregation is good for everybody.
If we had a good method for people to indicate routes that they didn't want to be aggregated, then more proxy aggregation could be done safely.
If I may... The idea of using a routing registry for this purpose has been suggested before. I still think it is a valid approach. Could be very useful in assisting with better proxy aggregation for all.
--bill
Here here. This came up in response to an experiment on the routing table (http://routes.netaxs.com). But unless everyone uses an RR, it is not going to be a useful for building proxy-aggregations on the fly (i.e. without human checking and intervention). Avi