Arrays are simply a means of performing a vast number of parallel experiments in miniature.
Experiments that once would have taken days or years to conduct can now be done thousands of times over in a few hours and perhaps someday in seconds. Moreover, arrays promise to make something greater than the sum of their parts. A few transistors can make a nifty portable radio. A few million, a microprocessor. Similarly, microarray companies are making systems that will allow applications simply not possible through manual experimentation.