Should I build more circular train networks?

On my Scenic playthroughs, I discovered that ring networks may balance the load from each station from the network. However, it also decreases the efficiency when multiple Locomotives (instead of Carriages) are placed. Since Carriages are rare, when should I build more circular train networks?

Here's that Scenic playthrough. Note that the light blue lane has one locomotive, but it holds up relatively fine; The dark blue lane has three locomotives and it doesn't spread the load well. The yellow lane has a locomotive with a carriage and it works pretty well even when the passengers drop off to reach the Hospital (plus symbol).

Loops in Mini Metro are definitely beneficial.

1. trains can go in either direction
2. you can can control how many are going in each direction
3. it tends to reduce hot spots
4. with a single locomotive doing a loop should decrease the time between visits to the same station.

The negatives are that it might:

1. make you use bridges that you could use elsewhere
2. in extreme mode loops prevent you from extending that line again. It is probably best to avoid loops in extreme mode.
3. take up extra passes through a station that would prevent a new line coming to that station after

I find that loops are so good in Mini Metro that I applaud real life systems that have evolved to include them (Chicago, NYC and Paris) and scoff at cities that haven't gotten there (LA, DC, BART in the Bay Area). It seems obvious from riding BART for a couple of years that a loop would improve reliability and reduce hot spots.