My personal experience is no different then what is described above, i.e. out of four institutions I teach at, two don't have any lab assistant, one always seen busy in his seat and can troubleshoot only "not working" issues, one is aloof of his core work but apple of eye for management and out of the lab staff; rarely work in the lab, mostly unavailable to teacher and students while walking tall as granted a lab supervisor status.
Another major issue with the management while hiring a computer lab assistant is that they look for a computer technician and they totally overlook the Computing 9691 demands. For example, apart from his HW and networking skills if teacher and/or students require him to give support for practicals in programming then he should be capable enough to do so.
Lastly, I request schools, colleges and institutions not to treat computer lab assistants just as a troubleshooting guy but someone who is same as other sciences lab assistants, who after teachers briefings can not just help arrange practicals but also in the absence of teachers could support students with their practical related queries too.