Hi Pix,
Well i personally feel that apart from Faulty TRX troubleshooting ,prefmark can be very useful at times even if u r having normal SFH(1*1 or 1*3).At places where the azimuths are not standardized and hopping frequencies are very much interfered due to overlapping of coverage area of diff cellshaving same FHS(and there r plenty of such cases in my current network and operator doesn’t allow redesign :P)…you cannot do much as whenever the call goes on hopping, the Rxqual degrades(6,7).So, simple solution is to push traffic to the BCCH TRX by just change of PM 🙂
Vice versa is also applicable at certain cases.