In 32-bit XR, also called cXR for classic xr, uses admin mode to control shared resources like fabric, fans, power supply, etc. Early on in the GSR/12k and CRS days we had a concept of SDRs or secure domain routers, basically you add more than 2 RPs or dRPs and they control some LCs in the chassis(s) while other RPs own other LCs. The fabric etc is still shared between all SDRs. Each SDR has its own login if you have root-lr access, root-system access gives you access to control the admin mode configuration. So in short the difference really is if you need SDRs you need to define users in admin, otherwise it doesn't matter where you define the user. In case of the first user generated by the system it has to be in admin mode. eXR also has SDRs but only on NCS6K. As well no other cXR platforms have SDRs.
Sam
