[Jtsummers]

It made more sense when I followed some other links in this discussion. Read this:

  Hey.

Or this exchange:

  Statement: We got the tickets for tonight!
  Response: Yay.

It comes off as very flat or dry. Unenthused. A plain "Yay" with no punctuation would be better here. I wonder if this is the context that we're missing and others aren't providing, because I almost always use punctuation, including periods, in my messages. No one has ever complained. But with short messages, like these, I would never use a period. For full sentences, however, I can't think of any occasion outside being rushed where I wouldn't end it with a period.

[oytis]

IMO, it looks dry, because an exclamation mark would be more appropriate. If you just omit the punctuation, it can be interpreted as if you omitted the "!", but with the full stop you explicitly say that you don't mean "Yay!".