Some part of it stops working.
It may only affect something really obscure and not be noticeable except for some kind of erratic error - or it may just die.
Various series of CPUs over the years have had alternate versions with parts disabled, like cache RAM or whole cores in dual- or multi-core devices shut off, as parts of the IC did not pass testing during manufacture.
If I remember right, the first Intel "Celeron" series were Pentiums (or some series) with disabled cache, sold at a lower price.
And some of the AMD FX four or six cores, 8 core devices with failed cores disabled.
The idea goes back decades; I believe it was the Sinclair Spectrum that used faulty 64K RAM chip that had either the upper or lower half usable, as they kept the cost down.