The biggest advantage of touch screens is that they are infinitely reconfigurable. So things like phones where you can have dozens of different types of applications running in the span of a day they provide a clear win.

Another advantage is that you can share control space with display space but I think this is rarely a big advantage (other than the benefits described above in that you can reconfigure what is control-space and display space).

For most devices that aren't general purpose computers I don't think touchscreens are beneficial. For example in a car there isn't that much variability in what you do so there is little benefit of a touchscreen so it doesn't outweigh the downsides.