The reason removing the HD 4870 made compiling shaders take longer, is the Intel HD Graphics is built into the CPU. It now had to perform rendering, and compiling shaders on the same chip, that is what slowed it down. 
The reason removing the HD 4870 made compiling shaders take longer, is the Intel HD Graphics is built into the CPU. It now had to perform rendering, and compiling shaders on the same chip, that is what slowed it down.