You could. What folks are saying is that most modems might have 10/100 ports for Ethernet speeds or they might have Gigabit Ethernet maybe.
A separate Ethernet switch known to be able to run Gigabit (or if you were doing something called “bonding” of Ethernet ports technically it has to run faster than gigabit speeds) plugged into one of those ports and then everything that needs fast access to the NAS plugged into that, eliminates the speed bottleneck of the built in switch inside the modem, if it has a bottleneck.
Kinda like building your own little local racetrack with an off ramp to the modem and the internet via one cable, since the internet pipe itself is very rarely gigabit speeds and the modems they provide often can’t go that fast either, internally.
If the modem has gigabit Ethernet ports it’s free to try your way first and measure the maximum file transfer speed. Many “gigabit” devices will really run about 300 megabits per second maximum if they’re old designs.
To go gigabit a little desktop gigabit switch is cheap. To start doing “bonding” of Ethernet ports into one fatter pipe requires a little more expensive switch.
And then, unrelated to home gamer setups usually is cascading multiple switches in a building and figuring out how fast to make those links and blah blah blah... you get that idea. We just put in our 10 gigabit backbone and switches that can handle that at work in the building as we built out part of the warehouse into office space.
And then there’s switches that can power things like phones with power-over-Ethernet from each port, yadda yadda yadda.
We’ve come a long way from my early days when a 10 megabit per second hub cost thousands of dollars. Most of this stuff is well below $100 for home use now.
We had a co-worker come ask us one day... “What Ethernet cards do you guys use in servers?” As we dug into why he was asking, he had built his own firewall for home using pfSense (smart guy!) and then moved into a house that has true gigabit (actually 2 gigabit if he pays for it!) internet speeds over fiber (I’m jealous!).
His cheap five dollar gigabit Ethernet cards in his mini PC running his firewall started “smelling bad” a few days later. Yep... they were overheating to the point they smelled. Given a few more days they probably would have let their magic smoke out, but he stuck a DC fan next to the thing and was blowing on them.
We laughed and told him to buy a couple of nice Intel cards for a few bucks and no more smoking home firewall. Hahahah.
Long story short, SOME consumer grade stuff can’t really do gigabit speeds. That’s why folks are saying you MIGHT need a desktop switch next to your modem.
