When I took my NACD cave class, my instructor insisted that I do dive planning sheets and check them against V-Planner. During training, the exercise can become a valuable tool for visualizing the dive, verifying certain aspects of the plan, and making sure you haven't missed any details. I'm not just talking about things like gas management or mixes or oxygen/nitrogen loading and the info found on the sheet, but the time that it takes to complete will often focus the mind on the dive plan long enough to create a pretty detailed mental picture of anything you may have left out.
When I first started teaching technical diving I employed worksheets because they were educational. Students seemed to develop greater confidence in their math and planning abilities when their calculations and the dive planning software used were very similar. They gained a greater understanding of how a neo-Haldanean model and a bubble model will approach the decompression curve.
I got away from sheets and just focused on using dive planning software and ratio decompression, but discovered that most of my technical students who have come from GUE nearly fail the written examinations for advanced nitrox and trimix. For example, if a question asks the student to calculate the EAD of Nitrox 32 at 100 feet and determine the decompression plan, nearly every GUE student will mentally do a 20% reduction in depth, arrive at 80 feet and plan the dive as an 80 foot dive. In reality, the correct answer would be 81.48 feet and would be rounded to 90 feet on a table. For this reason, I'm bringing tables and planning sheets back to classes.
While battlefield calculations are excellent to use underwater and ratio decompression allows a dive team to intelligently change the dive plan underwater, it's unfortunate when those awesome "on the fly" tools create confusion or mistakes in the proper use of basic dive tables. Newer tech divers, or even recreational divers who haven't purchased computers yet, might look to experienced technical divers for help with dive planning. Basic dive planning and table use should be learned well if for no other reason than to help others safely plan their dives.
For experienced technical divers, thoroughly using planning sheets and tracking your RMV from time to time helps you assess your abilities as you age or as your fitness level changes. Some people may still think their RMV is like .4 twenty years later.