I still need to search OSS note for this. The root words is "parallel depreciation" if you want to search further. Yes, it is required if you handle parallel currencies. You will not be able to activate fixed asset accounting in the company code via OAOB tcode if you do not manage parallel depreciation area and your company has parallel currency.
I would like to comment on your statement:
Because if we stick to the fact that this area is just a copy of 01 with no posting, no pb of reconciliation with FI may occur...
The main depreciation area is Book 01. And book 01 is required to have postings unless you limit the postings via transaction type. You cannot create a parallel depreciation area without referencing it to Book 01.
If you are expecting group currency postings in FI, you should create depreciation area that will represent that postings in Fixed Asset.