I have a Dell laptop (Inspiron N5110) and apparently it came with 2 graphics cards. When I run lspci | grep VGA, I got this output:
00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
01:00.0 VGA compatible controller: nVidia Corporation Device 0df5 (rev a1)
I wanted to play with some 3D software, not run fancy games, but view some 3D files. And I kept getting errors about Xlib not having a GL context (or something). I didn't want to use the hardware accelerated graphics, because those drivers are often rubbish on Linux, I just wanted to use Mesa, and do it all in CPU. It might not be fast, but it will work.
To enable only mesa, run this command:
update-alternatives --force --set i386-linux-gnu_gl_conf /usr/lib/i386-linux-gnu/mesa/ld.so.conf