RenderTexture.GetTemporary
static function GetTemporary(width: int, height: int, depthBuffer: int = 0, format: RenderTextureFormat = RenderTextureFormat.Default, readWrite: RenderTextureReadWrite = RenderTextureReadWrite.Default, antiAliasing: int = 1): RenderTexture;
static RenderTexture GetTemporary(int width, int height, int depthBuffer = 0, RenderTextureFormat format = RenderTextureFormat.Default, RenderTextureReadWrite readWrite = RenderTextureReadWrite.Default, int antiAliasing = 1);
static def GetTemporary(width as int, height as int, depthBuffer as int = 0, format as RenderTextureFormat = RenderTextureFormat.Default, readWrite as RenderTextureReadWrite = RenderTextureReadWrite.Default, antiAliasing as int = 1) as RenderTexture
Parameters

width Width in pixels.
height Height in pixels.
depthBuffer Depth buffer bits (0, 16 or 24).
format Render texture format.
readWrite sRGB handling mode.
antiAliasing Anti-aliasing (1,2,4,8).
Description

Allocate a temporary render texture.

This function is optimized for when you need a quick RenderTexture to do some temporary calculations. Release it using ReleaseTemporary as soon as you're done with it, so another call can start reusing it if needed.

Internally Unity keeps a pool of temporary render textures, so a call to GetTemporary most often just returns an already created one (if the size and format matches). These temporary render textures are actually destroyed when they aren't used for a couple of frames.

If you are doing a series of post-processing "blits", it's best for performance to get and release a temporary render texture for each blit, instead of getting one or two render textures upfront and reusing them. This is mostly beneficial for mobile (tile-based) and multi-GPU systems: GetTemporary will internally do a DiscardContents call which helps to avoid costly restore operations on the previous render texture contents.

You can not depend on any particular contents of the RenderTexture you get from GetTemporary function. It might be garbage, or it might be cleared to some color, depending on the platform.