Rhenny
Adventurer
That is one thing I like about the Starter Set adventure. In several places where encountered could be linked there are explicit reasons given why they will not (e.g. waterfall drowning out the sound, some monsters always making a lot of noise so others ignore fighting in that area etc) or possibly that fighting in one area will attract the attention of a specific area. It also has places where it says that guards are lazy and don't really pay attention.
All of those things (from Cragmaw places) could be good to take inspiration from to avoid large encounters. Maybe one patrol stays away to prevent a two-front assault or similar.
This is a very good point.
In many of the adventures I create and run, I think this through before hand as well. Quick examples I've used off the top of my head...
In one area some of the npcs/monsters are using pick axes to try to dig through a wall or mine gold/gems. Lots of noise...they won't hear fighting in nearby areas.
In one area, npcs/monsters are drunk and passed out. No response to nearby noises.
The thick walls, doors or tunnels in this area prevent even noises from combat from carrying past area x and area y. Sometimes winding tunnels do the same thing.