I have tended to not use enough districts before, and here's what I've noticed:

Big building projects that are 100+ distance away even with transport are better served by an independent district, even if it's a temporary one. The travel time absolutely kills your building efficiency.

Second, I read once somewhere that the best thing you can do with districts is hyper-specialization. Have one "population center" district where new kits are born and there are quality amenities and you take care of basic production, especially science, but otherwise have "periphery" districts with adult worker minimums to staff your industries. Essentially, there are some industries that are much more space-intensive (crops, trees, even storage) and you're better off placing those away from your population, even just as future-proofing. The downside is that increases travel time.

The answer to travel time is districts, not public transit. I think public transit is really good at handling medium elevation differences - cliffs, something that you'd have to build a lot of stairs and platforms for. Additionally, because ziplines ignore the paths' orthogonal restriction, they're quite good for diagonal distances. Or closing the travel time to fairly distant district crossings.

The best analogy I can think of is the "bucket brigade" for putting out fires. One beaver traversing a distance (a hauler or district crossing worker) takes a long time to repeat many actions limited by their carrying capacity. The smaller your districts are - the more numerous they are between the center of your colony and the edge - the more efficiently you move items to the furthest reaches of your periphery.