Just a note: if you have to render video (regardless of whether or not FCP, or any NLE for that matter, can play back the footage with an RT preview) and you choose not to, you always run the risk of losing quality and dropping frames. This is the whole reason the clips need to be rendered. FCP will automatically render things that need to be rendered to ETT at full quality (unless you change this under the RT settings).
In Final Cut Pro there are render notification bars at the top of the timeline just above the timecode ruler. The top line is for video, the bottom is for audio. If thee bars are any color other than gray (native playback), purple (referencing full quality render files), or diim green (full RT playback), then rendering is necessary to ensure full quality, full frame rate playback. Bright Green indicates preview quality, but this is in no way full quality even though you see video playing back in your canvas.
If you want to ETT with an unrendered sequence and be notified of dropped frames, go to your FCP user prefrences and make sure that ‘Report dropped frames during playback’ and ‘Abort ETT/PTV on dropped frames are checked.’ The first option will let you know while you’re editing/playing back a sequence if drop frames occur (so you’ll know you need to render that section). The second does exactly what it says – stops those operations if dropped frames occur while those operations are in session. If you don’t want to be notified, turn those options off. Turning off the second will allow ETT/PTV to continue with dropped frames, possibly causing stutter and sync issues that will not necessarily resolve themselves once playback returns to a less processor intensive section of your sequence. Keep in mind though that even if you don’t get dropped frames, you may still only be recording preview quality footage, recorded at the full frame rate – you will not get a warning for this.
Best,
Ben