What are examples of when seq_along works, but seq produces unintended results?

Question

What are good examples of when seq_along will work, but seq will produce unintended results?

From the documentation of ?seq we

Answer 1

This should make the difference clear. Basically, seq() acts like seq_along() except when passed a vector of length 1, in which case it acts like seq_len(). If this ever once bites you, you'll never use seq() again!

a <- c(8, 9, 10)
b <- c(9, 10)
c <- 10

seq_along(a)
# [1] 1 2 3
seq_along(b)
# [1] 1 2
seq_along(c)
# [1] 1

seq(a)
# [1] 1 2 3
seq(b)
# [1] 1 2
seq(c)
# [1]  1  2  3  4  5  6  7  8  9 10

It's probably worth noting that sample() exhibits similarly crummy behavior:

sample(a)
# [1] 10  8  9
sample(b)
# [1]  9 10
sample(c)
# [1]  8  7  9  3  4  1  6 10  2  5