Azure Blob Storage offers two different storage tiers based on the data access frequency and purpose. It’s the IOPS capability of the tiers which differentiate them. Cold tier is suitable for less frequently accessed data like Archive, backup, Compliance on hold contents, disaster recovery data sets. While Hot tier is meant for live data that will be frequently accessed by user or application.
While Cool tier is cheaper, you need to make sure it is utilised for the right scenario. if you have an IOPS hungry application it may suffer performance loss if you put it on a cool tier.
If you need Cool tier provision your storage account as Blob Storage account as against the General Purpose Storage account which does not offer these tiers within that blob. Cool tier pricing slabs can be seen here
Find below a quick comparison on the tiers