I have a medical condition where I cannot just tilt my head back to swallow. Using a water bottle is problemmatic unless I stop the bike, lean my body backward. I can suck water from a hydration pack while riding.
I also have difficulty getting a water bottle from the cage and replacing it due to frequent hand numbness. When I had looser cages, I had too many problems with the bottles launching themselves.

I have a couple of hydration packs for long summer rides or for rides when I do not want to slow down or stop to drink.
I use the extra-large one for riding rural areas. There are no opportunities for refilling water within a couple of hours. Frozen water in insulated bottles on the bike frame will be hot and unpalatable in 2 hours.
I use the smaller hydration pack for supported event rides where I can get refills.

A hydration pack filled with ice water is also cooler than having the sun beat down on my jersey-covered back.

When riding with a hydration pack, I only put plain water and ice in it to avoid cleaning issues. I carry a small bottle of extra-strength electrolyte solution and a flask of gel for fuel. I also carry a small bottle for plain water to help refill the hydration pack, pour water over my head or for cleaning. The bottle rides empty at other times.

I tried keeping the hydration bladder in the freezer between rides, but the gasket tends to freeze shut and the bladder will be a little disformed. It worked out better for me to completely empty and air out between rides and refill before riding.

The hydration pack can be a nuisance for me to fill at my office for after-work rides and sometimes from motels. So I rely on bottles when I am not riding shortly after leaving my house.