This means that if you print on the correct side the curl from the laser printing process is canceled out by the curl in the page, and the result is a flat sheet. But, if you print on the wrong side, the curls add together and the result is a very curled sheet. Just like any other purchasing decision, what paper to choose depends on the output you desire. Ideally, when it came time to print you would have several different papers available and you would pick the best one for the job. While this is the best solution, most people do not view it as a practical option since they do not want to have to store many open packages of paper.
Multipurpose paper is the least common denominator of papers.
It is inexpensive and will work passably in both laser printers and ink jet printers. It will feed through laser printers and accept toner, but it is generally lower brightness, lower weight, and less opaque. A sheet which is more opaque is harder to see through, making the text easier to read. Also, using multipurpose paper might result in some printing defects. For those reasons, multipurpose paper would be ideal for faxes, drafts, and other documents where the actual appearance of the print is not so important, but where cost may be a factor.