Could you clarify, what may be an issue with more connections, and how a managed switch solves it?
Managed switches give you nice easy "plug-n-play" setup. You don't have much to configure because the switch just acts to connect the clients together.
A managed switch is more useful in a larger and more complex network. Maybe you don't want every client to see everything.
One of the more useful features is VLANs (Virtual LANs). You can segment the network so each port only sees traffic bound for a particular VLAN. Let's say Seyed's network had a large amount of remote Ethernet I/O. And Let's say his SCADA station is also bandwidth hungry. In an unmanaged switch all traffic is seen by all ports. With a managed switch, you could configure two different VLANS which would segregate the Remote I/O from the SCADA station, so that none of the remote I/O's packets would be transmitted to the SCADA station thereby reducing traffic on that segment and vice versa. If your I/O was sensitive to latency (such as a motion control) you don't want to flood that segment with the data being transferred between the SCADA station and controller.
Similar would be QoS or Quality of Service, which could prioritize certain packets over others, such as prioritizing motion data over production data to accounting.
Managed switches can be configured to provide basic security by restricting MAC addresses that allowed to communicate. I've heard of more than one system brought down because someone plugged in a laptop to an empty ethernet port and flooded the network or worse, injected malware. But I'm paranoid.
For troubleshooting the ability of a managed switch to "port mirror" a port lets you see exactly what data is being transferred on a particular port.
Managed switches can also be configured for redundancy. So, if part of the network goes down the switch can reroute traffic.
Managed switches can even be remotely managed and monitored, useful if you have a full-time IT department to handle this kind of stuff.
In Sayed's case, I don't think these features are needed. He isn't planning on connecting to another switch (or if he is he hasn't told us). There is only a few clients and there should not be any bandwidth problems. Troubleshooting should be trival. So, a managed switch is not necessary. I don't think he wants to have the trouble of setting up a managed switch either.
Now, the reason I would consider a managed switch is I'm familiar with their setup (which is important as they are not plug-n-play) so the additional setup time minimized. I also want to create future expansion capability. I'm always being approached with "we need (want) to add this feature or another." For example if a year down the road Sayed's boss says "I want the SCADA station to connect to our production database via the enterprise network (or worse to a remote site)." There might be too much broadcast traffic on the enterprise network for the machine to handle.
