Data has a temperature. A log file just uploaded is hot. A log 30 days old is warm, occasionally pulled up for analysis. A log more than a year old is cold, barely looked at except during a regulatory audit. And a log five years old is in the Ice tier, retained purely out of legal obligation.
S3's eight storage classes are a trade-off design of cost, availability, and retrieval time mapped onto this temperature spectrum. The wrong class choice quietly eats money. Put hot data in Glacier and you rack up excessive retrieval costs; leave cold data in Standard and you waste storage cost