That's interesting. After reading this discussion thread, I went and read all the links people have provided and then looked at RB (Runtime Broker) in Process Hacker.
This is on a laptop running on Win10-64 Pro v1511 Build 10586.0 .
RT seemed to be using very little (around 0.03%) or no CPU, but was sitting on about 935Mb of Private Memory. The laptop has 2 x4=8GB RAM, so RB was using nearly 12/5% of RAM.
In System-->Notifications & actions-->Quick actions--> Notifications, the first 4 of the switches were ON, and the fifth was OFF.
I found that switch #1-Show me tips about Windows seemed to affect the RB process most, so I restarted RB via Process Hacker and experimented with switch #1. Restarting stopped the process, but did not cause the process to start up again though.
It seemed that switching switch #1 ON or OFF would trigger RB to start, if RB was already stopped when the switch was pressed. RB would then stop itself again after about 30sec., if the trigger to start had been moving the switch to OFF, but would continue to run if the trigger had been the ON switch.
With the switch ON and RB started, I ran a steam game program that always crashed when initially started, sending notifications to the screen display and the Action Center window (click the icon above or next to the Start bar clock to bring that up).
This gave RB something to be busy with, but it's use of CPU seemed to very briefly dynamically change somewhere between (typically) 0.2% to 5.0% at the most, and RAM would dynamically change between about 1.7Mb to 11.0Mb, at most, and settle down at about 2.0Mb when RB was idle at 0%CPU.
So I do not know how RB accumulated the 935Mb of RAM, though I have the idea that maybe it is buggy, or some apps are not playing nicely with it, and it somehow gets hooked on to and progressively accumulates RAM without it being dynamically reallocated/released to the system. That might also explain an odd performance issue - hesitation - that I have experienced in this laptop's operation, when nothing seems to be hammering the CPU particularly hard. I didn't consider that one of the causes could be that available RAM might be running low and a lot of memory page swapping to/from disk might be going on.
I shall have to figure out how to automatically monitor the RB process more closely from now on.