The Multiband Limiter splits the incoming signal into different bands according to the settings of the crossover stage and limits them individually afterwards before they are summed up again. This signal processor is normally used for mastering a mixdown to bring a lot of loudness and power to your tracks. It keeps the signal always below the threshold to prevent digital equipmenmt from clipping.
This limiter uses lookahead technology to prevent your signal from getting distorted. That means that the signal is getting delayed by a few milliseconds when it is processed. Keep in mind that the delay it produces is two times the lookahead time you set.
With the weight coefficient you can give importance to signals you don't want to lose in the limiting process. E.g. if your high-mid band (containing most of the vocals) starts fading in the background from now and then turn up its weight to let other bands process the gain reduction for reaching the desired limit. Your vocals will remain in the foreground even if heavy gain reduction is necessary. Values below zero will remove weight from a band and means "prefer this band for gain reduction when it comes to harder limitation". The weighting is affecting all bands equally, so setting all knobs to 1 has the same effect as having them all set to 0 - that is to say none.
The ASC (Automatic Smoothing Control) produces soft gain reduction even if the signal is reduced permanently. Normally the release time would try to reduce the gain reduction to 0 in the set time while a steady reduction (because of hard limiting) needs a release time to the average gain reduction instead of no gain reduction. The result is a slightly smoother signal even on heavy gain reduction. Control the ASC effect via the ASC Level setting. ASC depends on your release time settings and slightly extends the desired time value depending on the average gain reduction. Disabling ASC will result in a slightly higher loudness for the cost of some smoothness. It may be preferred on harsher material.