Dropbox's PHP SDK heavy-handedly suggests that one should use Composer to install and load their SDK. Also, version 2 of AWS's PHP SDK also offers Composer as a installation/loader (fortunately without the bias).
I'm using the Codeigniter (CI) framework which has several simple mechanisms to load modules. It has 1) a built in "vendor" folder (called "third_party" by CI, "vendor" by Composer). 2) "helper" and "library" folders to control modules I've created, e.g., $this->load->library("blah_blah");
3) Lastly, nothing prevents me from writing vanilla PHP include/require "blah/blah.php";
statements for edge cases.
I don't know other PHP frameworks well, but I'd assume they handle dependencies in similarly simple manners as this would seem one of the main purposes of using a framework.
In light of all this, are their additional benefits to Composer beyond what the frameworks provide? Or to replace the parts of my code that talk to my framework with that that would work instead with Composer? In general, am I not understanding something about Composer?