Can I delete Sony FS7 .mxf video files after import?

Is there any compelling reason to keep .MXF files (from Sony FS7) once they are imported into FCPX?

Is the video quality 100% identical, or is it transcoded? Is it just rewrapped from MXF into Quicktime? I notice that the QT files are a little bit bigger.

I don't have any experience with .MXF, but I believe FCPX simply re-wraps files on import, leaving 100% of the quality.
The quick time files may be bigger because it is transcoding compressed audio into some form of uncompressed audio.

One reason to keep the files would be for backup purposes.

Not all MXF files are of the same flavor, and it's possible that not all of the metadata in them are carried over with a re-wrap to Quicktime. They may also have clip spanning information that is necessary to combine shorter clip segments into one longer clip. With that said, if your quicktime mov files that were created upon import seem to be intact and correct when you view them, and any metadata you need is present, there likely would not be any other reason to keep them. As mentioned, for backup purposes I would generally keep a copy of the original file and card structure aside from the copy of the mov files created upon import if the content is important. Quality should not be any different, also as mentioned. If you optimized the footage in FCPX upon import, that would have created larger edit friendly versions of the clips.

Thanks! That's why I love this forum. I couldn't find an answer when Googling, but you guys answered right away.