Well, for one, dust. There's a strong case against mounting the electronics on a piece of wood and hanging it on the wall in open air, but if the builder is odd

Well, for one, dust. There's a strong case against mounting the electronics on a piece of wood and hanging it on the wall in open air, but if the builder is oddly inflexible on that point then liquid-cooling is probably the most practical way to avoid the daily-or-more-often process of removing dust and debris.