Blizzard Entertainment is in the process of rolling out a high bandwidth server option to Overwatch. It was something that was part of the Overwatch beta. At the time, Blizzard said that they would investigate adding the high bandwidth option to other game modes if it performed well and players responded positively to it.
Keep in mind that this is being rolled out and may take a few weeks for it to appear on all regions. Right now, they are rolling out the high bandwidth option globally to PC. (Overwatch is not compatible with Mac). Blizzard is exploring how they can bring the high bandwidth option to console.
In the official post about this upcoming change, Community Manager Lylirra explains more about what the high bandwidth option means.
So what does that mean? In Overwatch, our high bandwidth option adjusts the game’s client update rate (the frequency at which your client gets updates from the game server) from 21 updates per second to 63 updates per second. This reduces the amount of time between when you complete an action and when your client hears back about the result, which in turn will help make the game feel more responsive.
In addition, Blizzard is adding in “tech that will automatically and adaptively scale down your update rate if we find your connection can’t keep up.” They are looking to add an option that will allow players to self-limit their update rate in a future patch. The reason for that is because Blizzard recognizes that “not all internet connections are equal”.