Any multilingual person that consumes foreign media targeted at the local market knows that official subtitles are hit-and-miss, sometimes writing down something that sounds the same, but it's not (where/were) and in some cases even reversing the meaning of the sentence. Fansubs, on the other hand, if they are for popular media they have outstanding work poured into them, and when it is for niche media they might be slightly lower quality, but in those cases official subtitles are not available at all in the first place.

Next time I'm in Japan, I plan to look for and buy a DVD for which I made fan subs.

If a DVD has subs, chances are the pirated versions of it contain the ripped version of those subs. Fansubbing generally refers to making subs for material that has no subs at all, or not in that language. OCR-ing some captions or subs and pumping through Google translate isn't exactly fansubbing.