Is this normal for FCPX? Even if I make the smallest adjustment, the video has to render.

Just FYI, I'm running on an i5 iMac with 24GB of RAM and have all my media stored on a thunderbolt external drive.

You can turn this off, if you wish, or change the timings in Preferences for FCP X under the Playback heading.

Is this normal for FCPX? Even if I make the smallest adjustment, the video has to render.

Just FYI, I'm running on an i5 iMac with 24GB of RAM and have all my media stored on a thunderbolt external drive.

If you have added filters or done anything to alter the original video, then yes, FCPX will want to render again. Video that is not altered, just dropped on a similar format timeline (size/frame rate), will not need rendering except with transitions.