What are the disadvantages of a mini PC for a business?

Assuming you mean a USSF or smaller.

There are not many actually, which is why so many are used in business environments.

Others have mentioned the lack of expand ability - so you really need to know WHAT you need when you go out to buy one, as there is little or no scope to add anything afterwards.

If you want to upgrade the graphics, you will have to hope it works with an GPU.

In my mind, for pure business use, you have to carefully consider what CPU to go for; not just for longevity; but because the bigger cpus draw more power and create more heat, so the fans have to work hard to keep it going.

And the fans in these cases have to be small - and that means very noisy when their speed is raped up.

You CAN get small, efficient and quiet Noctua fans, but I don’t know of a system builder using them - they aren’t cheap - and retro fitting isn’t always possible.

There are many mini PCs coming in from China that are basically laptops with no screen, they tend to be a lot quieter, but remember the CPU inside are “m” versions, so are a computationally a lot less powerful than the desktop versions, and so may run out of steam in a couple of years, due to software bloat.

Pick the right one, and it will do the job you want for 10+ years; pick the wrong one and you will be looking to replace it in 2 years.