The problem with these methods is that they slow down as more and more accurate results are needed and as the number of particles increases. At finite temperature the computer time scales exponentially with the number of degrees of freedom and inversely with the temperature. Full explanation of the released-node method. Extension to excited states. Bayesian methods can extract can be used to extract more information for the transcient signal.
Cancellation methods work by allowing positive and negative walkers which annihliate when they meet.
That they can work mathematically is not in question. The problem is to show that they scale in the limit of large system size. Original development of the cancellation scheme for model problems. J. B. Anderson in Understanding Chemical Reactivity , S. R. Langhoff, Ed. Rev. Formulated problem but no practical examples except for a single particle.