This might help explain the functions of the Sends:
Automating audio changes in the Audio Mixer
You can use automation to apply changes to an audio track’s settings as a sequence plays back. You can automate the volume, pan, and mute settings of a track or its sends. For track effects, you can automate all effect options, including the bypass setting.
Automation modes are set in the pop-up menu at the top of each track. For example, with automation set to Latch, Touch, or Write, drag a track’s volume fader or pan control during playback. When you play back audio with a track’s automation pop-up menu set to Read, Touch, or Latch, Adobe Premiere Pro plays back the track with the automated adjustments. As you make adjustments in the Audio Mixer, Adobe Premiere Pro applies your changes by creating track keyframes in the Timeline panel. Conversely, track keyframes you add or edit in the Timeline panel automate values (such as fader positions) in the Audio Mixer as the audio plays back.
For each audio track, the selection in the automation options menu determines the track’s automation state during the mixing process:
Off Ignores the track’s stored settings during playback. Off allows real-time use of Audio Mixer controls without interference from stored automation settings.
Read Reads the track’s automation settings and uses them to control the track during playback. If a track has no settings, adjusting a track option (such as volume) affects the entire track uniformly. If you adjust an option for a track that’s set to Read automation, the option assumes its former value (before the current automated changes were recorded) when you stop adjusting it. The rate of return is determined by the Automatch Time preference.
Write Records adjustments you make to any automatable track settings that are not set to Safe During Write, and creates corresponding track keyframes in the Timeline panel. Write mode writes automation as soon as playback starts without waiting for a setting to change. You can modify this behavior by choosing the Switch To Touch After Write command from the Audio Mixer menu. After playback stops or a playback loop cycle completes, the Switch To Touch After Write command switches all Write mode tracks to Touch mode.
Latch Identical to Write, except that automation does not start until you begin adjusting a property. The initial property settings are from the previous adjustment.
Touch Identical to Write, except that automation does not start until you begin adjusting a property. When you stop adjusting a property, its option settings return to their previous state before the current automated changes were recorded. The rate of return is determined by the Automatch Time audio preference.
If you want to preserve the settings of a property, right-click an effect or send and choose the Safe During Write command from the pop-up menu. This command prevents that property from being edited when Write automation mode is on. It also protects that property across all tracks in a sequence.