I will give you a perspective using my job as an example. I do tech support for storage products for everything from small business to large data centers. To some of my peers that means checking out only the storage device and turning people away with an issue if the storage device reports no errors. Having at least a basic all around skill set with most of the things your customers connect your product to is priceless and makes you much more efficient at your job and gets you better survey scores than your peers (good for when raise time comes around or when applying for a promotion)

Often I get calls such as "our iscsi storage is not reconnecting or performing slow since we had a power outtage. I think I need a new storage controller" when what actually happened is the running switch config was not saved so the switch went back to factory defaults and lost config when it powered back up. Some of my co-workers are too nervous to touch a switch because they have never played around in a switch cli. That often means calling the switch vendor to open a ticket and a long wait time while your customer is down. Businesses hate being hard down. Downtime costs a lot of money. You are their hero if you can fix something that is not even your product line and get them back in business much faster than they could have opened a ticket with the other vendor. Also there's a good feeling of pride when another vendor calls you saying 'we ruled out our product (os, switch, etc) and everything points to YOUR product causing the issue so we have conferenced you in with the customer so you can fix your stuff.' Then once you confirm your product is good you look at the other vendors stuff and find whatever they missed. The customer says something like "wow, you support blah better than blah supports their own product." The rest of the call becomes very awkward for the other company after that :)

If I had to tell a new guy what to get familiar with at my job it would be this.

Networking: Cisco preferably. It is the most common in data centers and it's cli is basically the industry standard. If not Cisco then used Dell switches are cheap and cli is close enough that if your comfortable in one you can stumble your way through other brands with the help of Google.

Hypervisors: Get familiar with ESXi. At least 3/4 of the companies I work with are running VMware esxi for a hypervisor. HyperV is in 2nd place and everything else falls in the remaining 1%. This subreddit loves proxmox but this is the only place I've ever even heard of it being used so it's just not worth my time to touch it.

OS: Get to know windows server. By that I mean try to set up a windows cluster and set up roles like active directory, dns, exchange, etc. Some Linux/Unix experience is good too because you will need it occasionally.

I know things vary depending on what job your after but hopefully this was somewhat helpful.