Multipart uploads start to become valuable for larger files (100 MiB+) as it uploads a single object as a set of parts. This has certain benefits, such as improved throughput (uploading parts in parallel) and quick recovery from network issues (only the failed parts need to be retried). The downside is request overhead, as it needs to do creation, signing (unless you are signing on the client), and completion requests besides the upload requests. For example, if you are uploading files that are only a couple kilobytes with a 100ms roundtrip latency, you are spending 400ms on overhead and only a few milliseconds on uploading.