What is it?
The UDM Pro is a multi function small business device that:
- Is a network gateway.
- 8 port managed switch.
- Network Controller Application
- Unifi Protect for CCTV Security Surveillance
- Unifi Access for physical access control
Need more than 8 ports
If you only need the 8 ports then no you won't need another switch. But if you need say 10 ports then yes you would have to buy a switch.
But you would use 10 ports on that switch and none on the UDM Pro why?… we'll get there.
Faster than 1Gbs
The provided RJ45 ports are 1Gbs, The SPF is 10Gbs.
Power Over Ethernet (POE Power)
These ports don't supply POE, That's caused some debate as it would be a handy feature but on balance I think it's a good thing why, I'll tell you in the next section.
That little technical detail.
Data moving between ports on a switch is free, but any internet access or cross VLAN traffic will have to go back to the router.
What is the result.
To my way of thinking there are many types of switch and you will know what switch your particular use case will require. So while on one hand might you might only have 2 camera's, 5 access points and a computer or two. Another equal situation might be where you have 30 camera's and 100 access points, so we need to consider all the wide spectrum of uses.
So to answer the question although with the lack of POE, I think it's the result of a balancing act between cost, how it will be used and performance. Really 8 ports is never enough so I would opine that most of the time the answer will be yes - you will need a switch.
So why have the switch at all?
For small situations it's actually fine most internet connections aren't that fast and it's very rare to find sustained data rates so why not? it meets some needs without adding a lot of cost, and for one specific situation it's perfect.
So what would you use them for?
It comes down to one word - “Management” - as your network grows you inevitable add devices such as servers that have some for of network connected device management such as iDrac, IPMI or plug access for the console.
There are other uses as well so it can be very handy and convenient or just a stop gap as things grow.