Short answer: Yes, if they work for your project! Long answer:
The problem with free fonts
Paid fonts bought at a reliable source have the benefit of being tested and approved. These fonts are well designed and don’t have any glitches. If you buy a font you don’t really pay for the font, you pay for the guarantee that your fonts work the same way on the web, in print, and in many different file formats.
Free fonts don’t offer that guarantee.
This means that you must test and check free fonts yourself before delivering designs using them to your clients. This process will cost you additional time (and sometimes grey hair).
The benefit of free fonts
The main benefit of free fonts is … they’re free.
Another benefit is, that you can find many more free fonts as paid fonts online. By using them, you’ll automatically have a bigger selection to choose from and keep your initial costs low.
If you’ve found a free font that is perfect for your design project, and you’ve tested it thoroughly, why should you not use it? In design, the result counts. How you’ve arrived at that result is nothing your client really worries about. So, why should you?
Uniqueness is no reason to use paid fonts
Free fonts can be used by anyone, which is why it is tough to create unique designs using them. But most paid fonts aren’t expensive, which is why they can be used by almost any designer as well.
The only chance to have a font that is in itself unique: You must create your own font.
Some companies did exactly that. The German car manufacturer Audio created the “Audi” font for their own logo design. In the end, Audi gave away the font for free to anyone who wanted to use it in personal projects, but for commercial use, Audi holds the rights to the font, to keep people from copying their design.
Most companies can’t afford such a luxury. The font alone can’t create uniqueness in most projects.
This is another reason, why paid fonts don’t really offer any benefits besides the fact, that they are tested in detail by the platform selling it. If you don’t have to rely on that, give free fonts a shot.