Many config options depend on other options is unrelated submenus. As a result, people have complained about not being able to select the desired option because they finding all dependencies is too complicated. Select solves this problem and creates a near-identical new one. Now it is just as hard to turn some options _off_ as it was before to turn others _on_.
[ ] CONFIG_FOO If you enable this option, you will also enable CONFIG_BAR. Or : [x] CONFIG_BAR If you disable this option you will also disable CONFIG_FOO and CONFIG_FOO2.
Difficulty is somewhat increased by the number of tools that require such functionality. Support for xconfig and menuconfig appears to have priority as those users have a harder time grepping the kernel.