There’s a tipping point as Shane points out that will be different based on code type, drive speed, drive connection speed, resolutions, etc. Native codecs have better performance than non-native. Native codecs can be seen when doing a transcode and you see the list of what you can transcode to. For example, ProRes has recently been made a native codec. Anything else is being managed by the plug-in that creates another layer to play through.
Add to that the need for multicam or not, etc. will usually drive a decision to transcode up front, or at the end. H.264 is not a native codec, and as a codec is CPU intensive, so don’t expect a lot of “performance” with longer clips and bigger projects.
Michael