Straight tail tips generally denote directional, free-ride usage. So technically, it wasn't built for freestyle. Doesn't necessarily mean you can't do park with it. You'll just have a harder time jibbing with it.
There really is no functionality for a straight tip. The upcoming 2011 Burton Ration even gives you the option to cut your own tip and tail shape.
Now, if you have a swallow tail snowboard, that is a different story. The upside down V-Cut in swallow tips give you better control for turns in powder.