Belt balancing is necessary when unloading trains, as otherwise uneven consumption can lead to some chests/wagons running out of resources but the train doesn't leave because other wagons are still full.

For mining outputs, it can also be nice to avoid the outpost getting slow/stuck (never able to fill a train) when ore runs out for the outer lanes of miners.

Anywhere else, balancers are unnecessary and just serve to obfuscate a lack of resources.

(But if you really want to play without any balancers at all, that's quite possible: the train problems can also be solved by letting trains leave on a schedule independent of cargo status. All remaining balancers, including those on mining outposts, can be replaced with priority splitters.)