When I converted to DCC about a 18 months ago I installed three circuit breakers. One in each of my power districts, aka blocks.
I turned on all block switches and have run merrily ever since.
While circuit breakers are not required in DCC, as the DCC hardware contains its own fast acting breaker, having a breaker with a lesser amperage in each block eliminates having the entire DCC system shut down when there is a short.
Only the block in which the short is located will shut down. This requires the circuit block breaker to trigger before the system circuit breaker.
Each of my breakers are less then 4 amps while my Lenz 100 DCC system is rated at 5 amps.
So while not required, I do find the multiple breakers helpful in locating shorts and not shutting down the entire layout.
I use the breakers from Tony's Train Exchange.