Hi everyone
I just unpacked my newest switch. It should go into the living room. Unlike my other Mikrotiks, this one unfortunately has a fan.
Under RouterOS, it got so quiet it was inaudible. Unter SwOS it’s very audible. I doubt SwOS lets me fiddle with the fan speed, so what do I do? Use RouterOS anyway and deal with the headache of too many options or do I rip out the fan and replace it with something less noisy?
I’d go with ROS without a second thought.
CRS310 can be quite a beast of a router when running ROS v7 (with L3HW) … when you only need the device as a (higher-end) switch, this may compare to a a pile of chrome and huge alloy rims on a family sedan … but why not if it’s for free? 
I always assumed SwOS being way simpler might also lead to less CPU load and thus power consumption but if it’s too dumb to regulate the fan then yeah, RouterOS would be an option… but again, now I’ve got to figure out RouterOS…
If configured properly, then handling of actual traffic would be done by switch ASIC in both cases. The difference is in management (but that’s only effective when management is on-going … and normally thats very rarely) or if device performs L3 functions (which are not available in SwOS so you can’t compare both OSes).
So no, running SwOS (as long as device is configured identically) doesn’t save much power (perhaps a few milliwatts … which are offset by running fan motors at lower power ).