What are the benefits of using summer tires?

You might get a little better fuel economy.

That means they are putting on normal tires in place of their snow tires. And regular tires perform better than snow tires in every measure except for snow and maybe mud.

Summer tires wear better in the heat and dry roads. The dry traction rating is better on most summer tires, important for steering and stopping.

Summer tires are sort of a dinosaur these days,

They were important back in the 1950s and 1960s when

(a) radial tires were just being invented and not yet proven)
(b) studded snow tires were legal

But nowadays, they’re definitely not necessary and somewhat of a pain in the ass.

Nowadays, summer tires are sport tires, with incredible traction and good tire wear. The trick is that they need to be warm to perform. Also, the treads would be optimized for traction (small grooves) and not hydroplane resistance (large grooves). So if you want to have fun driving during the summer, you would want summer tires.

Winter tires would have large grooves to channel out water and large blocks to grip snow. They are also more flexible in cold.

I remember those snow tires and swapping them twice a year and it was a pain. Snow tires aren’t cheap and to have to own 6 tires for your car as standard equipment not counting a spare also a pain. All season tires are the style now but possibly in some high snow volume areas snow skins are useful. If you thought your current set of snow tires would not safely carry you through the next winter of snow and ice, it was common to not even change out of them in the spring to A: Save wear and tear on your summer skins one time, and B: get the final use of the snows because they will be more than good enough to drive on in the summer, and C: one less PITA to pay the garage to put them on, (if you are the type who can’t change a tire, or two). Then you’d have a few months to save up for brand new snows before the first snow storm of the upcoming winter..