I'm actually pretty much against UUoC. The cat example is much more resilient to modification. For instance, there are usually natural modifications considering filtering etc.
Anyway, since he said number we probably want `nl` not `wc`.
Separating pipe-setup from processing is sound engineering to me and makes things much easier. For instance as I iterate, I will have cat piped to head piped to filter but eventually I'll take the head out and run the whole thing. That's a trivial ^W versus moving around arguments and worrying about arg order, etc.
I am confused. What's wrong with `wc -l < file | ... | ...`?
I know `< file wc -l | ... | ...` is identical because the redirection is done before the command is executed, but what does putting it in front help with?
Because I feel the other answers, though correct, are entirely missing out on clarity:
The first iteration looks like this:
<file head -n10 | grep foo | tr baz qux
The second iteration looks like this:
<file gzcat | head -n10 | grep foo | tr baz qux
It makes the change much easier, since the first thing written is the first thing that happens. In `gzcat < file`, the logical first step - reading and streaming file - is now the physical second step. Like a German sentence, whenever you want to prepend the file, you have to maintain an item in second position.
In this particular case, people (like me) would wonder, "what's the point" and then go searching for the details of how `cat` and `wc` work, assuming that there's might be a reason the original developer wrote this code, as opposed to the simpler `wc -l` (i.e. Chesterton's Fence).
People usually use it because piped input is a known interface, you don't have to go digging through a man page or help page to figure out what flag is needed to accept input from a file. "Data flows from left-to-right" is also very intuitive, and you don't need to know the specifics of how your shell interprets a command line to figure out where to put the input redirection in the case of a more complicated shell command.
The point is I personally find it more ergonomic. Just like how I'll take a slightly longer route to avoid turning directly across traffic or avoid a particularly dangerous intersection.
Also, context is really important. Not that people on the internet ever stop to think about what the context is that the person is writing the code in. I don't write bash scripts that run mission critical workloads. I just ad-hoc type stuff into my shell to produce output I need for stuff at the time.
Ah, simple :)