The 'full Zone System' is for B&W shooting and film development and printing. You do NOT have to utilize the 'full Zone System', you can use a very useful PART OF IT with even color transparency and color neg! Many photographers do precisely that, including me.
One fundamental and universally applicable part of the Zone System is to understand the zones of reflecitivity (brightness), and how they effect any reflected light meter, and what the meter is trying to do
- how a reading of a Zone VII item differs from a reading of the Zone III item, and how both differ from reading a Zone V item
- 'make whatever it sees appear as 18% tonality'
Another fundamental and universally applicable part of the Zone System is to understand that often the range of brightness in a full scene simply cannot be fit into the film (or digital) range, so you have to decide...
- what portion of that brightness range can be eliminated in the shot
- what zone to 'place' in the center of the range which does fit in to the film/digital
Chapter 3 and the first half of Chapter 4 of Ansel Adams' The Negative are very useful reads for anyone, not just B&W photographers!
You do not have to have a one degree spotmeter to be a practitioner of what I wrote above, but they can be very useful in making it easier to be more precise in putting that theory into practice. One degree meters simply allow smaller areas to be read than the broader so-called 'spot' meters built into many cameras.