#1e: The importance of buy-in.
Gaining buy-in is a key reason for communicating well. As you rise in an organisation, the outcomes expected of you outpace the growth in your capacity as an individual contributor. Conversely, if you seek to gain more organisational power, you will find this is accomplished through the efforts of others.
Implementing any non-trivial initiative requires buy-in. You need approval from your bosses to move forward. Gaining buy-in from your peers unlocks knowledge and unblocks certain approaches. And you'll also, importantly, need buy-in from your direct reports and those doing the work.
This ability to scale yourself and enact impactful organisational change is only possible through buy-in. Buy-in is enabled by good communication.