Utilization of Event Log

Question

There is few Articles about Event log & they are good, they describe well,

if our program get an error or any other case then we can write it into eventlog

but what is the utilization of it?

If it get problem we write on it but we can't improve our program.(may be i am wrong)

so why we write it??

I sure there has a good work which i am over look or don't understand.

Can any body help me please!

Thank you in advance!