This is a question we are often asked and the answer is "no one knows" - not even the armchair forum 'experts' who predict catastrophe or claim it can't work.
Any tuning will in theory, increase the strain on the engine and its components but take a look at how big the tuning industry is - its worth billions and thousands of jobs. There are hundereds of companies in th UK selling boxes and remaps, and many thousands across Europe and the industry has been about as long as motor vehicles. So would this be the case if tuning was bad news for reliability?
The majority of UK insurers are aware of tuning and will cover the modifications and motor manufacturers do not carry out a forensic examination of your vehicle to look for any tuning that could have caused a particular part to fail under warranty.
These facts suggest to me, that tuning does not affect safety or reliability for the vast majority of motorists. There will always be exceptions so no tuning company can give a guarantee (that's actually worth anything even if the claim to provide one. Why? Because there will be a big reduction in any payout for wear & tear so don't expect 'new for old').
Another factor is simply that more performance means you get up to speed more quickly so that though the engine is working harder, it is for a shorter time, especially on our crowded speed restricted roads.
MY VEHICLE HAS A HIGH MILEAGE - SHOULD I TUNE IT?
Age and mileage need not affect reliability - how the vehicle has been treated and maintained and where driven will have a much bigger influence on this.
For example a high mileage ex taxi would be much riskier to tune than a high mileage long distance motorway car.
Once a vehicle approaches 150k miles, I personally would expect to have to start spending money on it simply due to wear and tear so tuning may hasten the demise of some parts, but the chances are these may fail anyway. At leas,t once replaced, whether tuned or not, I'd not have to replace them again AND its usually much cheaper to keep a vehice you like on the road than replace it.Sadly. some owners automatically blame the tuning product for ANY engine related problems, egged on by other tuning companies keen to do down a competitor and the forum doom and gloom merchants. But we are confident that our products are no more likely to cause problems than any other makes and such problems that can be directly attributable to our products unproven.