Can you explain to me why either of these is useful?

I've somehow gotten by never really needing to pipe any commands in the terminal, probably because I mostly do frontend dev and use the term for starting the server and running prodaccess

Pipelines are usually built up step by step: we run some vague, general thing (e.g. a `find` command); the output looks sort of right, but needs to be narrowed down or processed further, so we press Up to get the previous command back, and add a pipe to the end. We run that, then add something else; and so on.

Now let's say the output looks wrong; e.g. we get nothing out. Weird, the previous command looked right, and it doesn't seem to be a problem with the filter we just put on the end. Maybe the filter we added part-way-through was discarding too much, so that the things we actually wanted weren't reaching the later stages; we didn't notice, because everything was being drowned-out by irrelevant stuff that that our latest filter has just gotten rid of.

Tricks like this `\#` let us turn off that earlier filter, without affecting anything else, so we can see if it was causing the problem as we suspect.

As for more general "why use CLI?", that's been debated for decades already; if you care to look it up :-)

I can imagine a pipeline where intermediate stages have been inserted to have some side effect, like debug logging all data passing through.