Your bike chain goes through incredible stress levels when getting ridden - as well as being in constant movement, the chain is also exposed to the elements being placed low on the bike. As you ride your bike, and as you rack up your miles - your chain, like other consumable parts on your bike, wears down. As the chain wears, gear changes suffer - and the worn chain can damage other components on the bike’s drivetrain. As well as potentially damaging other components on your bike, a worn chain will also provide very poor, sloppy gear changes.
The above chain gauges and chain wear indicators are all designed to tell you exactly when your chain needs to be replaced - ensuring you enjoy excellent levels of performance, whilst also protecting the drivetrain components of your bike.