I think in general the semi-cons tag is a bit vague and I never know what to expect when I see it. Cons/non-cons at least hints that the bulk of the story will be one or the other. When I see both tags I assume that one character is one, and a diff charecter is the other.

The capitalizing of male/female, etc. doesn't make any sense because it doesn't seem to be used consistantly. I've seen it mean that one character was dominant and the other a sub, but I've also seen it used to imply one character was adult and the other a child. The only thing that seem to be totally clear is the grouping of who will fuck who. f/f = two girl fuck, and mfm = two guy one girl threesome, etc. But M/f could mean mature man and underage girl, or Dominant man sub woman. I like seeing something like m/f D/s as two seperete tags for clarity.

The "snuff" tag isn't totally pointless. Far more often than not I've seen it implies death during sex specifically and is diff than a murder tag which could be death for any other reason. The clearest setup is probably a willing victim tag which I've seen before as "con snuff". There's no confusion that it's willing death during sex.

Whatever you choose, the point made about the tags being advertising is spot on. I am far far more likely to read a story if it's tagged than not, and of course more likely to read a story that has my fav tags.