Sure...if you have a concatenation, it will just join the two disks end-to-end. When it starts writing to the partition it will start on the first device and write the data. It will continue to do this until that partition has been used up, and then it will start writing to the second device, etc. This is the most basic way of getting a large partition from two smaller ones.

Stripes on the other hand, although they also allow you to have a large partition, the primary use is to vastly improve disk performance. The stripes are a pre-determined size which can be specified by the admin when the metainit is called. So for example if the stripe is 32k, and there are three devices in the stripe then the first 32k of data written to the metadevice partition would go onto the first device, the second 32k would go onto the second device, the third 32k would go onto the third device, the fourth 32k would go onto the first device again, etc, etc.
This means that when an application reads or writes a large file, all three devices can share the load. This would (in a perfect world) make the reads and writes three times faster than just having one device. So disk performance can easily be improved by orders of magnitude by using this method. It is important, however, to consider your data and how big the stripes are, as this can make a huge difference on the end performance.

I hope this helps...