Should workers always look forward to being complimented or encouraged by their employers?
I'll say as an employee, you shouldn't expect compliments to be given to you every now and then since you already are being paid for the work that you are doing.
But as an employer, giving out compliment to your workers does you more good than bad and since they're just words and it cost you nothing then I don't see a reason why you shouldn't do it. Compliments has the way of uplifting your workers and they become energized to do more work as they see themselves as one with the company, with more compliments your workers will see themselves as family (human) and this will boost the productivity of your business so why aren't you doing it more often.
We are in a society that feelings are being ignored and the lower class aren't being considered human as they are being used like robots that have no feeling and all they do is work, so when you make someone feel seen and appreciated for what they are doing I believe you will get the best out of them.
The compliment thing is true. Still, you are being too generous to employers with that "it costs nothing so why not" line. Generosity like that must be earned, and employers have not earned it. It means that is an oversight, does not it? They forgot a small optimization. It is not.
You are constantly saying to someone that they are good. Be sure to observe what sprouts in that soil. They gain confidence. Confident people negotiate. Confident people set boundaries. People who are confident know their value and they do it. In terms of control, it is better to leave people just a little bit unsure of themselves, rather than making them feel safe.