e2fsck: non-desctructive, informative mode only?

from the man page:

Note that in general it is not safe to run e2fsck on mounted filesystems. The only exception is if the -n option is specified, and -c, -l, or -L options are not specified. However, even if it is safe to do so, the results printed by e2fsck are not valid if the filesystem is mounted. If e2fsck asks whether or not you should check a filesystem which is mounted, the only correct answer is ``no''. Only experts who really know what they are doing should consider answering this question in any other way.

--
-n Open the filesystem read-only, and assume an answer of `no' to all questions. Allows e2fsck to be used non-interactively. (Note: if the -c, -l, or -L options are specified in addition to the -n option, then the filesystem will be opened read-write, to permit the bad-blocks list to be updated. However, no other changes will be made to the filesystem.) This option may not be specified at the same time as the -p or -y options.

This quote is confusing and seems to contradict itself.

It says with the -n option it is safe... but even so, " If e2fsck asks whether or not you should check a filesystem which is mounted, the only correct answer is ``no''. Only experts who really know what they are doing should consider answering this question in any other way."

Also, what's the point of the -n option if " the results printed by e2fsck are not valid if the filesystem is mounted."

The whole man page is double-plus unclear and doubles-plus geeky language!

Translation, please...