위해 and 위해서 usually are used in two different situations. One is for nouns, and the other is for verbs.
1.널(너를) 위해 준비했어. (I have prepared something for you) : as in a colloguial situation
2.그는 나라를 위해 죽었다. (He died for his country.)
3.학교에 일찍 가기 위해서 철수는 일찍 일어났다.(Chulsu woke up early in order to go to school on time.) : as in a colloquial one
4.정부는 빈민들을 구제하기 위해 새로운 계획을 준비중이다. (The gorverment has been preparing a new project in order to help the poor.) : as in a formal one
When 위해/위해서 is with nouns, they give no formal-only connotation to me. So #1 and # 2 are both completely OK. But for #3 they give a little weird feeling to me. As you see, the contents of #3 is within colloguial situations and the context of everyday life. In this case, if 위해 comes with verbs, it is not fittible so much. On the other hand, #4 sounds good, because #4 is intended for forml situations.
So, we can have a rough and general assumption that if 위해/위해서 get along with verbs, it have a formal connotation, and so it is not so good for everyday life. But it is required for formal situations. Why this happens? When we see #3 and #4 carefully, we can find out that the verbs turn to a noun, kind of gerunds in English. Although 위해 /위해서 are not 조사(helping words for nouns) , probalbly in effect they seem to have a quality of 조사, so they force the verbs coming before them to be transformed to nouns. I guess that is why Koreans feel a formality from the pattern of '동사+ 위해서', while not from '명사+위해'. The transformation seems kind of artificial, so it is good for the formal, but not welcome in informal situations.
The solution is simple. It is to avoid using noun forms of verbs. How? We have helping words just for verbs, which ,named 어미, are specialized for verbs and adjective. In the case of saying the meaning of 'in order to', I would say -려고, which is one of 어미.
학교에 일찍 가려고 철수는 일찍 일어났다.
I think it actually shares in a very simmilar preference in English to choose 'in order to' rather than 'preposition+gerund'
A.Chulsu woke up early (in order) to go to school on time.
B.Chulsu woke up early for/concernig/with intention of/ going to school on time.
C. The president met with his counselors for discussing what to do with the marvellous and charming monsters from the space.
I assume English speakers can guess what the speaker of B meaned, but feel less natural than from A. So do we. Probably I guess French also has different preferred grammar signals for nouns and verbs respectively.
P.S Please be cautious of my comparison of English and Korean above since I can not feel the exact difference between 'in order to + verb' and 'prepostion + gerund'. According to contexts in Korean there are many cases where the difference is so subtle that both are fully acceptable.
어머니는 우리를 먹이려고 매일 일을 나가셨다. (OK)
어머니는 우리를 먹이기 위해서 매일 일을 나가셨다. (Good. In this case for me this is better than the above. But prehaps many other Koreans prefer the other.)
엄마는 아이에게 분유를 주려고 물을 끓였다. (natural)
엄마는 아이에게 분유를 주기 위해서 물을 끓였다.(not bad, but less natural. Instinctly I would say the above for this content, and I guess most Koreans would be with me for this case. It could be possible in written forms, but ,I think, rarely in real conversations.)