Living in a small apartment in New York City, I have a limited space in kitchen with no dishwasher. That naturally leads me to the philosophy of "less is more". I like to use less tools as possible, it will save space and hustle to wash every parts of appliances. In fact, we can do the most of cutting, chopping, mincing, and peeling with a good selection of knives.
However, I have to admit that these slicers are truly helpful. It adds a variety of textures to your salad recipes. Super essential for a vegetable eater, and very common among Japanese kitchen. The top one makes flat and thin slices. Great for slicing cucumber, celery, radish, cabbage, zucchini and potato.The bottom one makes noodle-like shred. Great for shredding carrot, radish, and etc. Washing is as easy as a knife.
Key note: They are actually quite dangerous and easy to cut your finger nail and skin. So, try not to slice all the way to the end. It's a better trade to leave some than bleeding while you cook.