Looks like this is a topic where the solutions are all across the board.
It would seem to depend very much on sailing area and style what function a GPS (or GPS enabled phone) or chart plotter is asked to perform.
For the typical daysail on the closest lake (of moderate size) it may be hard to argue that it is essential to have a way to fix position; using the GPS as a log to tell speed over ground in real time is fun but hardly seems a critical need - I know I was able to estimate boat speed to within less than half a knot the first time a crew brought a GPS enabled phone on board. And a GPS does not seem much help in developing a feeling for the boat (same applies to reading the wind from the wave state - I don't bring my portable anemometer much any more).
For racing, the ability to review the race one more time is helpful, I find, but for me that review happens on land, and not in the boat. In other words, I don't need to know where I am, but where I was. The log function I run live, but haven't found that it helps me sail better. The DS responds so quickly to shifts and fluctuations in the wind that I've never been able to reliably relate GPS readings to changes in sail trim - because the wind usually isn't steady enough. (That's why people practice using matching boats that sail in the same wind). Our local races aren't under DS rules, so I could bring whatever I wanted, but I find reading a device during a race difficult and distracting. Using the GPS as knotmeter ist just about the limit, I've never managed to use heading information, for example. There's anyway so much traffic on the lake that any time spent looking inside the boat can be a gamble...
For extended cruises, or events like the Texas 200, I'd agree that there's a case to be made for viewing this as a required aid in navigating. I bought my GPS the first time I sailed outside my home territory. There are cases where navigation by landmark isn't feasible (featureless coast lines or extended shallows). Knowing where you are can be both more difficult and more essential in that situation. So, even if I'm a bit of a minimalist, I wouldn't argue against a GPS. I would not trust a GPS for navigation in narrow channels (no matter what the claimed accuracy happens to be). Too many of my GPS tracks (when sailing) seemingly have me taking a walk on the beach, and too many of my GPS tracks when biking along a river show me taking a swim... When doing critical navigation, being off by 40' to 100', is not acceptable, and even once is too many, so I always navigate those by landmarks or buoys (or, in boats so equipped, using the depth sounder).
What about chart plotters?
I've sailed on large and small boats that had installed or portable chart plotters. They are really nice when crossing (or sailing in the vicinity of) shipping lanes - very reassuring to see that neither the little boat marker nor the moving arrow is about to intersect, especially when you spot that tanker on the horizon that will magically be at your position in about less time than you can imagine.
I've also noticed how much the attention gets drawn into the device and away from the boat itself or the surrounding waters. The effect is worst for plotters mounted in front of the helmsman, but I've observed if for portable units as well. For me that is a big reason to not have a plotter on board. Not only because I sit behind a screen all day and like to use the boat to get away from all of that. But also, because lining up two arrows isn't sailing. When racing, if I watch anything, it would be tell-tales. When cruising, I would rather follow the wind shifts, than re-trimming my sails constantly so that I can sail a straight line. I prefer correcting the general course every once in a while, rather than continuously. With the immediate feedback from a device, there's always the temptation to do the opposite, to play a bit of a video game with the tiller as joystick. So, I'd avoid anything that distracts me from feeling the boat, reading wind and water.
Even in a small boat like a DS, I maintain that its possible to do any required navigation using the fix from a GPS plus a (laminated) paper chart. The lack of convenience of this method means that one would turn to it at some intervals, interspersed with longer periods of just sailing. Incidentally, for big boat skippers I have crewed for (in coastal waters), I've so far observed a noticeable inverse relation between their sailing skills and the number and complexity of electronic devices -- but admittedly my sample size is too small

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However, that's just my perspective.
Beyond the question of what device, chart source or software platform to use, I would be interested in whether, and to what degree, any of you have experienced that distraction I've mentioned, and whether you have any habits or techniques to counteract it, if you are even bothered by it.