If you mean the timing chain its in for the life of the engine normally.
They do stretch especially on modified/tracked cars that have been driven hard but not until very high mileage. The cam position sensor will come on anyway to let you know its stretched beyond tollerance.
Its not something you should really worry about.
We change them if we have an engine out along with the tensioner just to be sure. Right pig to do in position....but can be done.