Do you learn all readings of kanji

[Koreankisaok]

I am learning kanji, but I notie that some people wanna create mess by using some readings whic hare not used....
I am curently on site
jlpt-kanji.com
and I wil give you an example...
耗
JLPT est: 1
School grade: Highschool
Stroke count: 10
Meanings: decrease
Readings: カウ, コウ, モウ
Vocab lookup:Level 2 vocabulary
消耗 (n,vs) exhaustion/ consumption/ (P)
help
why do I have to learn such stupid readings like kau or kou if I cannot (I have not searched, but I am almost sure) find them in any dictionary?
for what are these readings?
I am just learning the readings I need ...
for example
you see word
口 こう く
the most frequently used reading is kou ...
ku is sometimes used too, but I thik you do not need to learn it , unless you will meet a word with this reading, because even if you know 50 readings...
you wil be helpless child, because you don't know when use which.......
and they always like write these stupid unused readings at the beginning!
as they would be so important!
JLPT est: 1
School grade: Names
Stroke count: 14
Meanings: thread, silk cloth
Readings: いと, カン, リン
Vocab lookup:Full dictionary search
経綸 governing
綸言 imperial words
綸子 figured satin
help
all these dictionary entries are read "rin"
so why they wrtie that there are readings like ito or kan?

I am confused.......

 

[JimmySeal]

why do I have to learn such stupid readings like kau or kou if I cannot (I have not searched, but I am almost sure) find them in any dictionary?

You don't.

so why they wrtie that there are readings like ito or kan?

Because all of the readings were pulled straight from Jim Breen's KANJIDIC, without any filtering or selection.