Posted this in the M3/M4 Post, but applies here also.
Wanted to share from pictures of a late-model M3 in the shop at the moment. This is your typical daily driver, which occasionally visits the track a 1-2 times a month. M3 has upgraded turbos and your typical supporting bolt-on mods.
We get a call that the car has stalled at the track, will not turn over. Fearing the worst, arrangements immediately were made to get the car towed to our shop and see what's going on. Right away, we can see the accessory belt is missing.
Usually when vehicle throws a belt, it's known relatively quickly as the accessory belt drives multiple items. Power steering gets heavy, alternator light illuminates or vehicle begins to overheat. However, with electric power steering and high capacity Li-Ion batteries, it's makes things a bit more difficult for the driver to tell right away
The main drive pulley is integrated within the harmonic balancer, as seen below. If a belt shreds and makes it way behind the balancer, it can quickly wrap up around the crank hub and actually get sucked into the engine right past the front main seal. Potentially, a recipe for engine failure.
Luckily, this was caught in time. The oil was drained, pan removed, & crankcase inspected. Fresh oil, front main seal and new accessory belt were installed. A VTT SplineLock Crank Hub and Crank Bolt Capture was installed to further bulletproof the bottom end.
While seemingly unimportant, an accessory belt in the oil pan can lead to all sorts of damage - including blocking the oil sump and depriving the engine of oil, leading to engine failure.
TL;DR: Don't become a statistic. Inspect your belts, follow regularly scheduled maintenance.