PS: I wonder why there hasn't been a class action tort case initiated for battery swelling. It seems common to so many models- even our 2006 and 2007 MacBook Pros had the problem. (Including with Apple replacement batteries)
Battery swelling can happen/can eventually happen...on any device that contains a battery (portable computers, tablets, cellphone's, smart watches, etc). This eventuality is more like "when will the battery start swelling" versus..."if a battery will swell".
Generally speaking the older the battery gets...the greater the chance for swelling to begin. I've had batteries that were years & years old...some had tons of battery cycles on them...and some had hardly any battery cycles on them (thus it's not strictly about the number of battery cycles on a battery either).
Now if a battery starts to swell (for example)...only 1-2 years since new (or even less)...then this might be a situation that would be unusual. Could be due to a manufacturing or design defect...but also possible something on the user's end could be responsible (such as maybe something related to the "quality" of the electricity in someone's area, power surges, storms, etc).
PPS: I'm typing this on a Mac with a battery that has been swollen for a few years. No disasters yet.
It is possible to use a device with a swollen battery for quite some time...but generally the battery will continue to swell...and could eventually swell to the point to exert enough pressure on surrounding hardware and cause damage.
For example...the trackpad on a portable computer may no longer be able to do a physical click...trackpad could be damaged, or logic board could eventually be permanently damaged. Worst case scenario...eventually the battery may start to leak...and cause permanent damage to anything the leakage touches. Or even explode/burst into flame (there have been these rare cases reported).
Swollen batteries not something to mess around with. Which is exactly why many postal services & shipping companies have very strict rules regarding the shipping of electronics (new or used) that contain a battery. Or even the shipment of just batteries themselves.
Nick