Chances are that when you think of threads you think of threads in which the pitch and the lead are the same.
An example would be 1/4-20 with both a .050 pitch and lead. However on a daily basis you may use multiple start threads far more than single start threads.
Multiple lead threads are advantageous because they allow far more travel in one turn than single lead threads.
Multiple lead threads are very efficient for certain tasks.
Normally threads are used to hold things together, multiple start threads are used to easily transfer motion. Threads can be created that allow even 10 times more travel in one rotation than normal. Calculating multiple start threads is simple and expediential; simply add another pitch for each additional lead required.