2. Users report that it started crashing sometimes in version V.

3. After lots of debugging, you discover an input that reliably crashes your program after 30 minutes.

4. A bit later, you discover that your compiler started compiling function f so that it no longer works with unaligned data/buffers of exactly 8 bytes/whatever.

5. At the start of main, you add a dummy call to f with data that reliably crashes if your compiler decides to do that optimization again.

6. The program has become worse: it now always crashes, independent of its input, but you don't have to wait 30 minutes before finding out. That makes it way less likely that you ship a binary again that has the problem. It also makes it easier to tweak source code/compiler flags/whatever until the problem disappears.

Is that perfect? Absolutely not, it is more something of last resort, but depending on the costs of crashing versus those of sometimes crashing half-way through a run, it can be an improvement.

(this technique also can be used when your code hits compiler bugs)