This Ableton Live walkthrough breaks down two quick but useful readouts in the Mixer's Volume display: the Peak meter and the RMS meter. Peak shows up as a green line and reacts instantly to sudden spikes in level, while RMS sits beneath it and gives a steadier read on perceived loudness, a distinction worth knowing before you start chasing levels on a mix.
It also covers the per-track CPU meter, opened from the Mixer's meter selector. Each track gets six small rectangles that light up to show its relative CPU impact alongside the overall load of the set.
Once you spot the track pulling the most CPU, freezing it or removing some of its devices is usually enough to bring the load back down, letting you keep working without constant dropouts or maxed-out performance warnings.