For more than a century, amateurs have collected nearly all the brightness data on record for hundreds of variable stars of several major types. The future is shaping up to be different. A CCD camera on a small telescope, combined with cheap, powerful image-analysis shareware, can measure magnitudes of much fainter stars much more accurately than can be done by eye. Amateurs, however, are working to keep up. That time may still be years away.
Most amateurs begin astronomy just as sightseers, and eventually they reach a plateau.
After a few months or years of pleasantly touring the celestial scenery, they may feel a need for more meaningful involvement. After all, a tourist can't be expected to gape at the Grand Canyon forever. Lasting enthusiasm, in astronomy as in anything else, comes from purposeful activity. For thousands of people during the last century or more, variable stars have provided that outlet. If you can find the Sickle of Leo you can find R Leonis, one of the brightest red long-period variables.