I've seen that there are people obsessed with kanji, and they are seen as kanji lovers, could you explain me why? and give me some examples of it? where is better to use hiragana or katakana instead of kanji because is odd use kanji?
Some people like difficult words. Some like to sound overly formal. It is the same in English as in Japanese, but English uses longer (or less common) words where Japanese speakers use more kanji to sound either smart or eloquent.
There are two other reason though. One is word/etymology/history-nuts. It's kind of like someone using 'ye' instead of 'the', but not that archaic. Instead of going back 500 years, the kanji usage might have only been uncommon for 60 or 100 years. They just want to sound a little old/quirky/nerdy/literary. Shiina Ringo's lyrics are good example of this.
The other is humor, but this more obvious. You can give any set of strange kanji any furigana (reading) you want if it is for the sake of reading. The kanji might be "Great Death Witch," but the reading is "mother." Kerorogunsou （ケロロ軍曹） does this a lot.
But to answer your question: find someone/a writing style you want to emulate. Use kanji where they use kanji. Use hiragana where they do. More kanji is not better. Just like English flows best with a mix of big and small words, Japanese is easier to read with a good balance of kanji and hiragana.