The pecl_http extension has a little gem that can be handy at times - HttpRequestPool. Using this, you can send concurrent HTTP requests and can gain efficiency in fetching non-related data at once. For example, from an external source if your application needs to retrieve an user's profile, their order history and current balance, you can send parallel requests to the API and get everything together.
His code shows three example connections to a made up URL on three different endpoints. With the HttpRequestPool functionality, all three can be requested at once and tracked to extract the response body.