If you rush Avowed without exploring, you're going to have an absolutely miserable time.

First and foremost, Avowed puts a lot of emphasis on exploration:

• A lot of sidequests can only be found through exploration, and not completing those sidequests is going to affect how the main story and even other side-quests play out.
• Enemies don't scale, but their levels greatly outpace how fast your character progresses through doing just the main quest. You are required to explore and find materials/cash etc. to upgrade your stuff and keep up with the MSQ levels.
• Your companions often have conversations after finishing side-quests. These conversations add a lot to their characterization - especially by adding context. For some companions these conversations are absolutely crucial to really see things from their point of view.
• The sidequests you discover are often quite extensive, without going into details I found a random NPC while exploring a cave with a bounty - and the quest chain it started expanded greatly on some key events from Deadfire. It also gave one of Deadfire's major characters some real closure. This quest was completely optional, and if I didn't like exploring I'd have never found it (at no point in the MSQ am I required to go into that cave).
• The unmarked/discoverable sidequests have a lot more divergent states based on player choice. Which is to say, these quests have a lot of different states based on choices the player can make at the end of them.
• Progressing down the mainquest without doing any sidequest is going to lock you into some terrible world states.

Edited: I personally love love love this system because it really makes exploration feel good.