Disadvantage : one TCH is reconfigured as a CCCH timeslot
Advantage : double the Paging, Access Grant and Random Access capacities.
It’s the only way to have big cell configuration (> 12 TRX) without having control channels congestion, so in my opinion it’s a mandatory feature. Especially when you add the PS Paging load on top of the CS Paging. The 9 CCCH per BCCH is a bit light.
Everything that allows more traffic capacity is a must-have 🙂 It gives you an immediate return on investment.
In B10, you’ll also have access to new counters to check the PCH/AGCH/RACH congestion more precisely (the B9 counters are not very reliable, as far as i remember).