Example of a code that can be decoded using bounded distance decoder
The simplest example is a repetition code. You encode the bit 0 as 000 and the bit 1 as 111. The decoder outputs the majority bit, which is always at distance at most $t = 1$.

As another example, suppose we encode 0 as 0000 and 1 as 1111. We can still correct up to one error (by taking the majority), but we cannot accommodate $t = 2$, since given 0011 we can't tell whether it came from 0000 or from 1111. Therefore we need to declare failure.