The LP-64 Multiband is meant to be used on the master bus, and generally goes before your mastering limiter to bring up average levels before going in to the limiter.
It is useful for bass-heavy productions such as dance music, where very hot kick levels trigger the compressor causing other instruments to wimp out. Compressing the low frequencies separately from everything else helps avoid that problem.
The LP-64 is a linear-phase effect, which means it introduces a lot of latency and it is pretty CPU-intensive. It should therefore only be used during the mastering process, after raising your buffer sizes. It should not be used as a track effect. If you need a multiband on individual tracks, use the Sonitus Multiband. IMO it is a better compressor anyway, and certainly a much lighter load on your CPU.