First of all, there is not one role for a system engineer. There is a lot of interdisciplinary knowledge to have. The goal here is to have a global vision of the entire network infrastructure. In order to build a coherent, scalable and functional network.
Managing and monitoring hardwares like servers, switches, firewalls, routers, computers, cameras, digital display, Wireless technology, copper an optical wiring…
Also installing and configuring softwares, users and computers management, VLANs, mails (on-premise, cloud or hybrid), virtuals infrastructures,..
All those examples are part of the knwoledge that a system engineer must acquire. Due to his global vision, he will be able to improve the network infrastructure.
A consultant must find a good balance between existant technology and what the client needs and can afford. Knowing the bests technologies is useful besides, understanding the customer’s needs is a top priority. Proposing the most efficient solution according their own use is the best way to see a company grows.
To resume, a good system engineer consutlant needs technical a lot of technical knowlegde. But, he also needs social understanding to fulfill his job.
That is why this job is so rewarding and complete.