Playing a
record at the
wrong speed is absolutely
vital for the art of
beat matching. As not every
track are the exact same
BPM (
Beats per minute), you need to adjust the
pitch so that you can line them up correctly.
Most modern turntables, such as Technic's SL-1200s, have a variable pitch control that allow the adjustment of -8% to +8%.
See Beat Matching 101: A dj primer.