Digital because;
-Convenience
-Slightly faster loading times if on internal memory
-Can keep game slot free for rentals
-Less cartridges to carry
-Can keep purchase concealed from partner more easily...
-Game can follow you around hardware now with better account management.
-You can't "lose" the game in the normal sense.
Physical because;
-You have something physical for your purchase/collection.
-More room on your internal memory for other games that can only be downloaded...
-You have an asset that you can use if necessary.
-Nintendo are still a long, long way behind the competition on account management, even if it is improving.
-Nintendo products become very collectable quite easily. Especially as the physical market is being reduced, having something to share with future generations that might not be available could be useful.
-You can't "lose" your purchase if in ten years Nintendo suddenly decide to shut down the store and your Switch needs to be replaced or repaired.
-You can lend it to friends and family to try.
-Not necessarily applicable to this situation, but the platform holder (Nintendo) has less control over the prices. They are notoriously stingy on the eshop.
-Cartridges are so small, carrying them around should be no problem.
That's all I can think of for now...