Most of the binary blobs in Linux are in device drivers, and most of those are in WiFi drivers. Their function is to be the operating code for the hardware on the device; unless they're loaded when the hardware is initialised, the hardware will not function. It is unfortunate that WiFi manufacturers, in particular, have chosen this method of operation; but they have. Different Linux distributions have taken different approaches to this.
Fedora ships blobs, having decided that 'everything needed to be free software ... it was a popular and well-received move, but it broke everyone's WiFi, because (at least at that time) just about every WiFi driver in the world required the loading of a binary firmware blob into the hardware. No one was keen to see Fedora become known as "the distro everyone used to use until they needed WiFi", so [they] changed the requirement to "must be free software, except for firmware needed to make free software work"' (full disclosure: I wrote that article).
Debian ships blobs, but is careful to separate them out as contrib or non-free, according to the availability and licence status of their sources.
Some, like PureOS, just don't ship them. The FSF maintains a list of these, which links also to their discussion of why some other distros (and some other OSes) failed to make the list.
As you have found, one consequence of using a fully-free distribution is that you have to be extremely careful what kind of computer you buy if you want to use WiFi. If you want to know whether any given system will run without binary blobs, you will need to find out the chipset of every single system component, and check that fully-free drivers are available for it. You will also need to run with the microcode that your CPU ships with, and you should expect to have lots of fun with your motherboard's BIOS. It is very unlikely any off-the-shelf system will meet these criteria, so you're likely to end up building your systems from components.
Personally, I wish that (WiFi) device vendors would stop doing this. But until they do, I am glad that free software gives me choices - I can decide how pure I want to be, and how much functionality I'm willing to give up in service of that goal. And so can you.