The DNA copying enzymes have a hard time working to the end of a chromosome. For circular chromosomes this is not a problem, since there is not a sharp 'end'. However, for a linear chromosome, without extra mechanisms in place, a bit of DNA is lost off the end of the chromosome after each replication. Because of this, eukaryotes have a telomere to cap off their chromosomes.
In most cells of a mutli-cellular organism, this telomere is slowly worn away after each reproduction leading to apoptosis. Cells that need to reproduce indefinitely such as germ and stem cells have to invest in extra mechanisms to replenish the telomere. For multi-cellular eukaryotes I can see how this might be usefull (for instance as a cancer counter mechanism). However, multi-cellular organisms evolved from single-cell eukaryotes.
I cannot see a reason for wanting apoptosis in a single-cell organism. However, single cell eukaryotes (say yeast) still have linear chromosomes with telomere caps. What advantage did linear chromosomes provide single-cell eukaryotes to offset the extra investment in reparing the telomere?