It depends on the procedure, somewhat.

For example, it's very tempting for a company to send out tests before doing much resume screening. Why should I spend 30 seconds looking at a resume when I could have the candidate spend an hour on a test, and save myself 30 seconds?

Or what if I set a take-home test which is supposed to take 1 hour, but also supposed to really to stretch candidates' ability and give the best candidates a chance to shine? Probably a lot of average candidates will give themselves a bit of extra time - and before you know it, I'm sending a "1 hour" test that takes an average of 4 hours.

Take-home tests are a lot less objectionable if you can properly guard against these problems.