The rentals are just there to take over for the main steam plant while the equipment is shut down. Steam is used for tons of applications, from energy generation, heating, manufacturing process, sterilization, food processing etc. You’d probably be shocked how many facilities have a steam plant, I know I was when I first got into this.
And yes, it’s a giant bomb that will level a building but it’s almost always a low water issue from poor maintenance or safety shortcuts when that happens. Throw some cold water on your hot grill and just imagine that effect in a contained vessel. But we call them “disturbances” or “puffs” since explosion is rather dramatic and tends to make people nervous and is extremely rare. These things don’t just fail or runaway on their own, there are multiple safety devices in place to ensure that doesn’t happen and when well cared for are as reliable as a good hammer.