This one is pretty easy, since the defaults tend to be sensible, for the most part. I have identified only three default services that may not be that useful to the average user.
The technique is simple. Open YaST, look in the “System” section and identify “Services”. This opens a window that does some checking, then loads a list of services that are available on your system. Consider these three:
iscsi — used only if you have networked SCSI drives using no other protocol
You can purchase boxes that house one or more SCSI drives with a network connection. Instead of being some kind of file server, you can connect directly to the drives themselves and mount them over your LAN connection. Without such a device, you have no reason to run this or the other services with similar names: iscisd and iscsiuio.
If any of these are running, select each one in turn and hit “Stop”. Then change the start status to “Manually” or “On Demand” — whichever is appropriate.
ModemManager — needed if you intend to ever use something like a cellphone or similar device to connect to the Internet
This allows you to tether your system to broadband cell devices, along with traditional hardware modems. It’s more likely to be useful on laptops than desktops. If you think there’s any likelihood of needing this service, leave it running. Otherwise, turn it off.
postfix — mail transfer agent, seldom used on desktop computers and virtually never on laptops
Unless you are running SUSE as a server and have need of a mail server, you can shut this one off.
There was a time when an internal mail server was the way to get messages from the system that would be of interest to power users. These days, just about all of that is handled via systemd and it’s journald. You can read up on that here. (I recommend downloading the entire SUSE Linux documentation package here (current version in a zip file) and keeping a copy if you plan to learn much about running SUSE.
