The Plugable DisplayPort to HDMI Passive Adapter is useful if you want to connect to a 4K@30Hz HDMI display from your DisplayPort enabled Mac and Windows PC. However, even for computers or tablets which can't output 4K@30Hz, you can still use the Plugable DisplayPort to HDMI Passive Adapter to output to your HDMI TV or monitor at lower frame rates and/or resolutions.
Just make sure that the computer supports Dual-Mode DisplayPort (DP++) when using the Plugable DisplayPort to HDMI Passive Adapter.