This clip from Ableton's Learn Live series covers two quick but useful ideas inside Hybrid Reverb's routing section. Switching between Serial and Parallel mode changes the fundamental relationship between the Convolution and Algorithmic reverb engines: in Serial, the signal flows through Convolution first and its output feeds the Algorithm section; in Parallel, both engines receive the signal independently, giving each its own character without one coloring the other.
The Send knob controls how much signal reaches the reverb, and automating it opens up a simple but effective compositional move. By drawing in automation, you can send only the first chord or two into the reverb, leaving the rest of the progression dry, which creates a sense of space that lands once and then recedes rather than sitting under everything.