I use it almost every day. I'm in the process (now in it's second year) of documenting a network with 1000's of devices connected to 100s of switches across 35+ IDFs in 5 buildings
That's a big campus!
The real benefit is being able to KNOW what's on the network and then respond appropriately. I've been able to identify countless network issues by finding PCs in VLANs meant for phones, finding IP addresses for security cameras that were "lost" years ago, documenting PC ages, etc etc etc.
Here's the strange thing about Local area networks. It's rare that you get to build a 'greenfield' campus LAN where you can do it right from the start, using protocols like LLMNR or CDP to auto-provision devices onto appropriate VLANs. I've only been able to clean-sheet design a network once in my 20 year career....
Typically IT guys walk into brownfield campus LANs where the business has already sunk thousands of dollars into their copper & fiber networks and has zero incentive to rip & replace every switch and every reason to make modest/incremental improvements.
Oh the horrors I've seen: blue Linksys access points attached to server vlans, enormous broadcast domains with PCs, android phones, servers, voip endpoints, scanners/copiers and Access points with no segmentation whatsoever. I've even seen places where cleaning staff would unintentionally create a network loop by plugging a single cat5e cable into two network drops in the wall, which craters the entire layer 2 broadcast domain on a campus. I've got scars, let me tell you!
In my work slitheris serves as a sort of first responder tool...the patient is on the ground bleeding, can't breathe, and has multiple injuries, so I grab Slitheris and get to scanning the patient. Yikes, that's bad I think, as I watch the devices cascade down my screen. The neat thing is that after I've cleaned it all up and properly segmented things, Slitheris shows me that too, in a much more simple way that nmap