Planned obsolescence is a policy of planning or designing a product with a limited useful life, so it will become obsolete or no longer functional after a certain period of time.
Many products particularly electronic gadgets become unusable after some period of time. A good example fo this is the desktop PC or laptop. After a couple of years, it is already too slow to be used by current or available programs which become too resource hungry that their specification are not anymore compliant to the software requirement.
Planned product obsolence is a manufacturer modus operandi to force consumers to buy newer products. As these products become unusable, they will just end up into the landfill or similar disposal process.
Another similar manufacturer tactic is selling their products at low cost and selling parts at prices more than the whole product itself. It may sound silly but this is true. A very good example of this is the printer.
An inkjet printer may only cost $35 a unit. But ink refills will cost $40 a pair (color & black) increasing significantly the Total Cost of Ownership. If you are the consumer, what will you do? Of course buy a new printer. Where will your old printer go? Your guess is as good as mine.
I have seen a TV documentary about the export of old unusable electronic products such as computers to an African country. CPUs, monitors and keyboards are being burnt to salvage the copper content of these gadgets.
Manufacturers should be made accountable for the disposal of their obsolete product. A product return scheme should be enforce by governments to force the manufacturers to dispose their own obsolete products. If these will be done, then manufacturer will think to extend the useful life of their product.