We (https://vcvrack.com/) do this and it works great for us and our users. Wouldn't give up the licensing scheme for the world. We'll soon release a proprietary fork (Rack for DAWs) of our GPLv3 software (Rack) as a new funding source. It's the perfect funding scheme and has no major disadvantages. The author makes profit from a fork of the software, which requires/causes the GPL version to be actively maintained (since new functionality and bug fixes of the proprietary fork often derive from modifications of the GPL software). And the user has a choice of using the open-source/free software, which they can freely run, review, modify, and share, or purchase the proprietary software. By Economics 101 theory, a "trade" is always mutually beneficial if the user's intrinsic value of the software is greater than the purchase price.
As mentioned by others, we can't accept patches to our GPL software without a contributor license agreement (such as a paid contractor position), so make sure you're aware of this before choosing the dual-GPL/proprietary scheme for your own software. This isn't a big concern for us because in my personal experience, a patch that actually saves me time in the long run is very rare (See Quality section of https://github.com/VCVRack/Rack/blob/v1/.github/CONTRIBUTING.... You get what you pay for.) But I'm perfectly fine with doing everything myself or through hired work.
As mentioned by others, we can't accept patches to our GPL software without a contributor license agreement (such as a paid contractor position), so make sure you're aware of this before choosing the dual-GPL/proprietary scheme for your own software. This isn't a big concern for us because in my personal experience, a patch that actually saves me time in the long run is very rare (See Quality section of https://github.com/VCVRack/Rack/blob/v1/.github/CONTRIBUTING.... You get what you pay for.) But I'm perfectly fine with doing everything myself or through hired work.