NTSC video runs at 29.97 frames per second. No human has dared create a timecode that counts hundredths of frames (it would be too confusing,) - hence we have drop and non-drop. Clock time (electricity) operates at 60 Hz but the NTSC standard television operates at 59.94 Hz. If you double 29.97, you get 59.94 - hence - two fields per video frame. For now, that's all we'll say about "fields". Because of this speed difference between 59.94 Hz and 60Hz, there is an expanding elapsed time difference between the clock and timecode readings.

Drop-frame timecode counts each video frame but when that .03 finally adds up to a video frame - it skips ahead (or drops) a number. It does not drop a video frame, it merely skips a number and continues counting. This allows it to keep accurate time. So if you're cutting a scene using drop frame time code, and the duration reads as, say, 30 minutes and 0 frames, then you can be assured the duration is really 30 minutes.

Non-drop timecode counts (labels) every single video frame and does not make any allowances for the fact that it is really 29.97 fps. Therefore, if you cut a scene using non-drop time code and the time reads as, say 30 minutes and 0 frames, this is not the actual running time of the scene. The total time must be converted in order to know the true running time.

=============================================
The aim of an argument or discussion should not be victory, but progress.
Joseph Joubert, essayist (1754-1824)

So overall, it's not really a big deal?

I'm not sure what you mean by "big deal". The difference can be significant but it doesn't change the look or work flow of your project, if that's what you mean. The difference can affect the time frame of your final project.

Ok, thank you!