It's for long term offsite backups/archival. If you need to retrieve lots of data from it on a regular basis (e.g. because of a single dead drive) you're doing something wrong.
If our office burns down, and I had our offsite backups in Glacier, the retrieval costs are peanuts compared to cost of losing the data (going out of business). If my home burns down, and I have my offsite backups in Glacier, a few hundred dollars to retrieve data would be nothing compared to the emotional loss of years worth of photos etc.
But I have triple copies at home - minimum - of almost all of my data (mirrored drives + regular snapshots on a third drive; and a lot of the stuff is also synced to/from one or more other computers), and similar setups at work: An offsite backup is last resort.
If our office burns down, and I had our offsite backups in Glacier, the retrieval costs are peanuts compared to cost of losing the data (going out of business). If my home burns down, and I have my offsite backups in Glacier, a few hundred dollars to retrieve data would be nothing compared to the emotional loss of years worth of photos etc.
But I have triple copies at home - minimum - of almost all of my data (mirrored drives + regular snapshots on a third drive; and a lot of the stuff is also synced to/from one or more other computers), and similar setups at work: An offsite backup is last resort.