Effect of VGA's attribute controller 'Color Plane Enable' register during text mode?

[superfury]

What does the Attribute Controller's Color Plane Enable register (index 0x12) do during text modes? What effect does it have to switch plane 0/1/2 off (set bit 0/1/2 to 0)? Just blanking the characters if they're missing (plane0=character 0=blank, plane1=attribute 0=black), plane 2=No foreground=Black?

Anyone knows what this affects during text mode? Does it need to be set to 0x?7/0x?F in order for output to appear at all (not taking Pallette #0 all the time)?

3C0h index 12h (R/W): Attribute: Color Plane Enable Register
bit 0 Bit plane 0 is enabled if set.
1 Bit plane 1 is enabled if set.
2 Bit plane 2 is enabled if set.
3 Bit plane 3 is enabled if set.
4-5 Video Status MUX. Diagnostics use only.
Two attribute bits appear on bits 4 and 5 of the Input Status
Register 1 (3dAh). 0: Bit 2/0, 1: Bit 5/4, 2: bit 3/1, 3: bit 7/6