I had similar experience – space limitations gave more freedom of word choice and segment structure transformation.
That’s useful for a translator.

Very good point. When I started translating, I also got most of my documents on paper — in my case, as thermal faxes. Ah, the glory days of deciphering kanji from smudged ink blobs…

Today, however, I get the vast majority of my documents in electronic, editable format (with some scans and non-editable PDFs), so in my opinion, clients who today insist on paying by target volume are just hidebound.

Charging by source length has a lot to recommend it. But I got my start in translation when most documents arrived on paper—some still do—and getting the source length would be a job in itself.