Why H264for proxy media

It's always been engrained not to edit H264 material due to the high-processor load. I am new to FCPX and trying to understand why H264 is used since it's not an edit friendly codec.

Many systems now have hardware decoding of H.264 and have no real trouble playing it back. It allows for significantly smaller file sizes than ProRes Proxy.

Okay, got it.. Thanks.

In addition to what Tom said, I'd add that though hardware is more capable nowadays, the support for using H.264- or H.265-based codecs is a lot due to marketing and maybe a bit more due to many users who just want to use camera recordings in FCP...

A benefit of transcoding to an Apple-flavored H.264 is that it is likely easier for FCP to handle than some H.264 footage directly from cameras.

Things become more "critical" when you are editing several angles of multicam footage. At some point, ProRes-based proxies or optimized media will likely outperform H.264. And, in recent versions of FCP, you have more options when choosing to create ProRes proxies. If you have the storage space, it's always preferable to use ProRes media in FCP. Testing typical configurations and comparing them is always a good idea when preparing to start a new project.

Food for thought...