Saves space and some sanity
We finally got some vlan switches in the place I was at in 2006ish. Before that we had two routers running OpenBSD with two 4 port ethernet cards each. The pile of switches and cables that were disgorged during the upgrade was significant.
It was so nice having one single cable going into each of the routers. The rats nest became downright manageable.
Unfortunately there are some things that vlans can't fix. The morbidly obese owner, who I will call Captain Fantastic, let his chain smoking, alcoholism and reality-tv-show-worthy gluttony gradually morph into extreme hypertension, congestive heart failure and narcolepsy. The aforementioned caused Captain Fantastic's brain to mostly turn off, which didn't mix well with his love for tax fraud and fraud in general.
 Captain Fantastic said it was "type 2" hypertension. I looked it up and the only reason it was "type 2" is because they stop counting at 2. I can't remember the exact numbers, but his blood pressure was something along the lines of 290/220. His legs lost all definition, no knees, no ankles, just two giant sausages.
 He'd nod off mid-conversation. I later found out that he could only sleep sitting up as the fat would completely prevent him from breathing when laying down. The fat gradually got to the point where it prevented him from breathing properly even when sitting. Since he'd never really sleep as sleeping and dying were pretty much the same thing he developed narcolepsy. Luckily the narcolepsy didn't prevent him from driving as he had preconditioned himself by frequently driving with obscene amounts of alcohol in his blood.
One night his wife found him, sitting and completely unresponsive. This was the second time they ambulanced him into emergency (are medical forklifts a thing?). I was told that the next day he was responsive and the heart surgeon paid him a visit (again). The surgeon told everyone to leave the room, closed the door and proceeded to scream very un-surgeon-like things such as "stupid fucking asshole" and "shithead" at Captain Fantastic.
 At some about two years before the business mushroom clouded Captain Fantastic decided he was a race car driver, bought a brand new ford mustang and spent the next one and one half years pouring money into the car. This is at a time when we could have heated the building with all of the bills containing phrases like "final notice", "legal action will be taken" and "some guys with crowbars are coming". He would always wear his Mustang Racing leather jacket and cap that must have required a small bovine genocide to construct. Then came the bills addressed to "Captain Fantastic Racing Company". I guess you can just start a blatantly bullshit company, request credit from local businesses and you'll actually get it.
Eventually came Captain Fantastic's plans to transfer ownership of his empire of shit to someone and then declare bankruptcy. The trouble was that no one would touch that steaming pile with an 80' barge pole. That was about when I bailed out.
Years later a mutual acquaintance acquired Captain Fantastic's hosting business. Captain Fantastic had managed to keep a hold of it by selling it to his wife before he declared bankruptcy and the government came around to perform a prostate examination with a shovel. The incredibly unreliable hosting company he had moved to after the last completely unreliable company went mammaries skyward had evaporated overnight. Captain Fantastic had no backups, but he did have ownership of all of his customer's domains.
Over the years I'd managed to wrestle two domains from Captain Fantastic after some of this customers had somehow managed to find me and threw themselves at my feet as they screamed, cried and pointed at their rag wearing, emaciated children. Getting the domains back took months and was about as much fun as trying to steal weapons from a police station, after phoning up said police station and telling them you're coming to steal their weapons.
And that's why VLANs are great!