These are also called "ice cream" scoops - though I rarely use them for ice cream. I think they were once used mainly in catering for portion control - and possibly are still used for that reason in industrial kitchens. With the great emphasis on plating, hard to imagine chefs these days using them for that purpose.
Where they do come in handy is for baking - portioning out cookies. (And most professional bakers do use them.) I also use them for my Meatball Soup recipe.
There are various types of scoops - with differing mechanisms. This website links to a chart that shows the scoop sizes, linked to handle colours. Some of the ones with coloured handles note the scoop yields right on the handle. For recipes I make often, I make a note on the recipe to remind me which scoop to use.