Yep, good point. They are useful when you want to change the whole text inside the delimiters (and IME, it's most of the times), but they do different things than cf( because they also change/delete text behind the cursor.
`c])` is also pretty handy when you're within a bunch of parentheses. For instance,
if funca(funcb(red, green), funcc(blue, yellow)) {
^
If you are where the arrow is, `c])` will change the second argument. If you were on the comma before it, `d])` will remove all but the first argument.
The % approach works only on one direction.