Data can be overstructured. That's as bad as too little structure, because it doesn't take exceptional circumstances into account. For instance, say you've decided that a postal address always consists of a street number (strictly numeric), a street name, a street type (eg "Road", "Street", "Avenue"), a suburb, a state and a postcode. Well, in this case, maybe you missed a street type in your list, which means a certain type of street (eg "Place", "Esplanade", "Boulevard") is excluded. Or what about unit numbers? They all share the same street address, but delivering to unit 7 is very different to delivering to unit 17. You get the point. You need to strike the right balance between structuring your data to give it meaning and consistency, and leaving it unstructured to allow for unforseen circumstances. It can be a tricky balance to strike.
Mokalus of Borg
PS - The worst part is that the right structure is always changing.
PPS - Everything is always changing.