Your strands of pearls are an investment. Dirt and grease may find their way between the pearls and wear the material upon which they are threaded. As the thread weakens, there is a chance of it snapping. A broken necklace can be repaired easily with stronger string to prevent future problems.
If you do wear your pearls often and to prevent necklace breakage, it is a good idea to have your pearls restrung periodically, once a year or so. Pearls are generally strung with closely tied knots between each pearl to minimise wear, separating each pearl and giving the necklace the maximum flexibility.
Knotting the strand between each pearl will prevent all of the pearls from falling off the strand in the event the strand breaks. Knotting also prevents the pearls from rubbing against one another and causing damage. A little care can go a long way toward ensuring that your pearls remain safe and bright for years to come.