What happens now is that people setting a POS network sometimes, instead of getting an electrician, do it themselves. Then they sometimes select a cheap cable to save expenses. Some of these cables are pretty bad. If so you may notice that your network tends to operate slow, so these cables should be replaced.
Yet, if they are good cables, the question of whether to replace these cables with a different one will speed up the network. The answer is maybe but probably not.
There are many factors here, but the big two are latency and bandwidth.
I like to think of the cable as a water pipe.
Latency would measure how long and rough the pipe is slowing down the water travelling through the pipe.
The electronic signals travel at about 200 million meters/sec. Thus Melbourne to New York is about .1 second. Few cables would cause a problem here.
Bandwidth would be the amount of water that travels through the pipe; the wider the tube, the more water travels through it.
Now in a POS System, we do not pass that much data around. As long as your cable is a cat6 or better, and we are talking just the POS software traffic, you will not have a problem here. Things may be different at home. Say one kid is downloading some movies, another is watching youtube, you are on the computer, and someone is watching the TV. Lots of signals, lots of bandwidth.
The last factor is that many other factors besides the cable can slow down your network, e.g. your switches and network cards.
So if you're replacing existing cable thinking you will significantly improve your speed, I would say you are wasting your time and money.
This is actually why electricians tend to use decent but cheap cables.