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.

You can easily change that first command with muscle memory. That's why I use cat $file| but I guess <$file would work too.

As per James Taylor's comment above, using cat means you can easily replace it with head e.g. for testing.

And not change anything else in the pipeline.