Provisioned IOPS volumes (io1) provide a consistent amount of IOPS for IO-intensive workloads.  When actual IOPS usage is near the limit for a volume, Blue Matador will warn you.

When your application needs to consume more than the provisioned amount of IOPS, disk performance will suffer. This will cause read and writes to both be slower on the affected EBS volume.

Since 2017, EBS volumes can be modified while still attached to an instance.  This is extremely useful for increasing IOPS capacity when running near capacity, and can be done from the AWS console or through the API.