Computers would be fast, but they are not infinitely fast. And memory would be inexpensive, but it is not free. Computing time is therefore a bounded resource, and so is space in memory. One should use these resources wisely, and algorithms that are efficient in terms of time or space would help one to achieve that.
Also, having a solid base of algorithmic knowledge and technique is one characteristic that separates the truly skilled programmers from the novices. With modern computing technology, one can accomplish some tasks without knowing much about algorithms, but with a good background in algorithms, one can do much, much more.
