multipart/form-data vs application/octet-stream

I'm creating a simple REST API for uploading files. From other API's I found they use "multipart/form-data" content type. But for me, it looks like "application/octet-stream" is much simpler.

If I don't intend to send any more form data with the file is there any reason to use "multipart/form-data" and not "application/octet-stream" ?

While you don't intend to send any other data together with the file right now, multipart/form-data would give you the possibility to add additional data later on if this is required (without breaking compatability).

Also multipart/form-data would make it possible to access the REST API directly by submitting an HTML form (see https://stackoverflow.com/a/4526286/693140).

Your API could however support both types by using the client's content type header to distinguish between them.