One-off metric values are rarely useful on their own. The real value comes when you can plot and see them over time; how they change, how fast they change, what their range is, and so on.

On Linux you can schedule a command easily with the cron command. By putting the AWS CLI commands in a script, and scheduling it with cron to run periodically, you can feed metrics consistently to CloudWatch, without the overhead of running a dedicated agent on your instances.