We are used to inserting small routines at the beginning of the default interrupt handler as an IRQ wedge. This has an advantage of being easy and not requiring any modifications to the part of memory occupied by the ROM.
But the default handler is responsible for cursor blinking, handling the screen editor and few other things. As we don't usually need them in our sprite animation, the default handler's code is just a waste of cycles and memory for us.
We have a simple routine wedged into the interrupt handler. It changes the border and the background color, executes a hundred nops and changes the colors back.
This allows us to see how much raster time it takes to run this routine.