It depends, documentation is organised very differently than SO. If you want to read up on how X works in general, then documentation style is useful; but if you want to find out a single narrow application of X, then stackoverflow style is useful.

For simplified example, if you want to find out what flag -wtf does in some unix utility, the man page would be useful; but if you'd want to find out which flags should be used to achieve WTF then you'd often need to read the whole documentation to find out - stackoverflow serves as a "reverse index" in this case.