Here's an invented sentence which might have come from Indiana Jones and the Crystal Skull:

"Dr. Jones only knows the location of the skull."

It has many possible interpretations:
Dr. Jones only (i.e. only Dr. Jones) knows the location of the skull.
Dr. Jones only knows the location of the skull (but he can't get there).
Dr. Jones only knows the location of the skull (but not the magic words to obtain it). [similar to above]
Dr. Jones only knows the location of the skull (but not the location of the key that unlocks it).

In spoken language we use inflection to make the meaning clear. We often misplace the "only" but it's not a problem. There is at least one instance of this in a Sherlock Holmes story, so this problem/usage has been with us for a long time.

In written language there is no inflection. When the subject matter is technical and of which the reader has little or no prior knowledge, the use of spoken-language patterns can completely mangle the meaning.

And that's why the ability to write clearly is important.

So there, nyah!