Some times it causes to have low Hand Over(HO) KPIs. Because unnessary neighbours always creates HO revisions and HO losts. As a results HO success get reduced.
With Ericsson experience, there are counters for total no of neighbour relations (NRs) in BSC and total no of measurement frequencies can be defined in BSC. With unwanted NRs these counters can be reached.
I think frequently you should remove unwanted NRs (Check stastics and remove NRs having low HO attempts)