Preview Functions Offer The Best Outcome
If you're trying to finish the color grading and adjustment on digital film before printing it on actual film, you know you have to add in the factor from a color look-up table (LUT) before you print. If you don't, the print will look terrible, and that could ruin the overall effect your film has on viewers. Using color grading LUTs is a standard procedure — one that has been done many, many times — and it's not really that risky if you know what you're doing. Still, it helps to preview the result before finalizing printing arrangements. Many newer versions of software now allow previews, and if you haven't upgraded, it's time to do so.
Reassurance Before Printing
If nothing else, a preview of the film after the LUT has been applied will reassure you that the final print will look the way you think it will. That eliminates doubts and lets you move on to your next project without worrying that you'll get the print back only to find something went wrong. Experienced colorists might not think this is necessary, but it's still nice to have the confirmation that all is well.
Sudden Solutions
Another reason to have a preview function is that, like previewing a written comment for a website, seeing a preview of the result could give you more ideas that work better than what you've used, and it can allow you to spot little things that might have missed your gaze before. While the first LUTs that you applied would likely work just fine, seeing that final product before it's too late to change it can help jar your brain a bit and let it come up with alternatives that might work better.
Teaching Help
Previews also help teachers show students why a particular LUT works the way it does. You could always just wait for the final print to come back and compare them then, but why? With a preview function on your software, you can show students how their work really affects the final view.
You can find both free and non-free LUTs for color grading online and through various companies. See if you can check out samples to find a LUT series that you can work with, and also take a look at new versions of the software you use. Once you upgrade and get that preview function, you might find that your work goes more smoothly.