Set this to true if you want texture data to be readable from scripts. Set it to false to prevent scripts from reading texture data.
In order for Texture2D.GetPixel, Texture2D.GetPixels, ImageConversion.EncodeToEXR, ImageConversion.EncodeToJPG, ImageConversion.EncodeToPNG and similar functions
to work, the Texture must be readable from scripts. The isReadable setting determines whether scripts can access texture data through these functions.
Textures are not set as readable by default.
When a Texture is not readable, it consumes much less memory because an uncompressed copy of the texture data in system memory is not required after the texture is uploaded to the graphics API. Readable Textures require an uncompressed system memory copy of the texture data so that once edited, the updated texture data can be uploaded to the graphics API.