A work sample is a (usually, hopefully) standardized piece of work you request from all candidates that mirrors the actual work they'd be doing on the job.
There's no reason a work sample needs to be so onerous that it costs you a weekend. What people forget when this comes up for discussion is that interviews are work. In fact, they are themselves onerous work, since they require you to be on-site and intensely engaged in ways you don't have to be to do the actual work of a job.
A work sample, on the other hand, can be done from your home, with a beer next to your laptop if that's how you roll.
The notion of audition work has definitely been abused in our industry. People get work samples that aren't standardized. They get work samples that are later ignored. Work samples don't have objective scoring rubrics. Some annoying companies assign new features for their products as "work samples".
Done carefully, though, with objective and predictable grading and calibrated to offset in-person interviewing time, they're superior to any process we have.