Can I delete fcpx optimized files?

You can safely delete Optimised files.

Select the Library and then select Delete Generated Library Files:

In the next window choose what to delete:

Always use the FCP App to do this and not through the package Contents.

Al

Depending on your computer and drive capabilities you should be able to work with the original media.

It's not a question of whether optimized or proxies are better, just a question of what you need for your system and your media. You may not need either. Many users work solely with the original media. Thumbnails have nothing to do with optimized or proxy media.

There are two places where you set how files are imported, in the Import preferences,

and in the Import window sidebar that reflects what's in preferences. If you drag and drop for import the Import preferences will be used.

What Al said, but you may need optimized media depending on what the original media is. You might need to optimize iPhone media, but not necessarily for all your clips. You can create optimized clips and proxies for the files that need it. Select the clips, right click and use Transcode Media.

Proxies are supposed to be faster.

You could turn off the creation of optimized media for multicam clips, and then if necessary create proxies for those clips involved. There is a setting in the current version that says “proxies preferred” so the application will use proxies when available and original media otherwise.

Ah multicam. That’s different. Yes, uncheck optimized for multicam. If the system needs help with playback. Create proxies for the multicam media.