For many years, a common approach to implantation failure was to transfer larger numbers of embryos; regardless of embryo quality. The result was that after many failed cycles, some women would end up with high-order multiple pregnancies (triplets or higher). Clearly, this is not a good price to pay for success.
If the presumed cause of implantation failure is the embryos, this approach seems appropriate, although it can backfire. Transferring more embryos will not overcome uterine or other implantation factors. With improved diagnostic tools for implantation failure, along with PGS to screen out abnormal embryos, it no longer makes sense to transfer large numbers of embryos, even in the face of repeat IVF failures.
One could argue that once chromosomal abnormalities (aneuploidy) have been ruled out, there is little value to even a second embryo. Certainly, it is not a good idea to transfer more than 2 at a time when PGS has been performed.