Sprite atlases

If you use a separate texture for each of your spritesA 2D graphic objects. If you are used to working in 3D, Sprites are essentially just standard textures but there are special techniques for combining and managing sprite textures for efficiency and convenience during development. More info
See in Glossary, Unity has to create and send a separate draw call to the GPU for each texture. As a result, performance can decrease.

To reduce the number of draw calls, create a sprite atlasGraphics: A utility that packs several sprite textures tightly together within a single texture known as an atlas. More info. 2D: A texture that is composed of several smaller textures. Also referred to as a texture atlas, image sprite, sprite sheet or packed texture. More info.
See in Glossary. A sprite atlas combines multiple textures into a single texture. Unity only needs to create one draw call for all the sprites in a sprite atlas.

Note: If you use the Scriptable Render Pipeline Batcher, the number of draw calls might not decrease, but performance still improves a similar amount.

For more information, refer to Create a sprite atlas.

Assigning sprites to different sprite atlases

To avoid Unity sending multiple sprite atlases in a draw call, the recommended best practice is to create separate sprite atlases for the following:

• Each set of sprites you use at the same time, for example a different sprite atlas for each sceneA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
  See in Glossary. This avoids Unity loading unused sprites into memory, or creating multiple combined textures for a large number of sprites.
• Sprites that need different compressionA method of storing data that reduces the amount of storage space it requires. See Texture Compression, Animation Compression, Audio Compression, Build Compression.
  See in Glossary settings. For example, create a sprite atlas for highly detailed character sprites, and a separate sprite atlas for less-detailed environment sprites.
• Frequently used and infrequently used sprites.

Additional resources

• Sprite atlas best practices in Unity 6 on the Unity YouTube channel
• 2D game art, animation, and lighting for artists