Advantages: switching to an equivalent dose of Valium from a short half-life benzo (this must be carried out gradually) virtually guarantees that you will experience no interdose withdrawal effects; switching from a very potent benzo to Valium allows for much smaller cuts to your dose (more frequent small cuts are better tolerated than less frequent large cuts); if you have had problems sleeping, you may benefit from the sedating effects of Valium.
Disadvantages: some planning is required with a switch to Valium (but we will help you with this); an equivalent dose must be calculated and tweaked where necessary to suit the individual; many doctors (particularly in the USA) do not support a switch to Valium; switching will likely add to the overall time taken to withdraw; a small number of people appear to not tolerate the switch to Valium very well (this sometimes might be due to the wrong equivalent dose being prescribed or a failure to tweak the dose for the individual concerned according to how they react).
Prof. Ashton achieved very good results in her clinic by switching patients to Valium. Usually, her patients had already failed to quit benzos via the Direct route. If your doctor is supportive, and willing to adjust the equivalent dose as required, you are more likely to benefit from substitution.