Are data packs on mobile are beneficial?

We often purchase data packs to reduce the data charges.

Have you ever noticed that when your data volume of the pack is used, generally you will not be informed by the network operator that your data volume has been finished or about to finish and ultimately you will be charged at higher rates.

Thus whenever you have subscribed to the data packs then be sure that you are informed or has self-made estimation that when data pack's volume will be finished.