Polytarp is a low-cost, durable and waterproof material. In addition, manufacturers can easily produce the tarps you require, based on your specifications. Therefore, you could easily use them for large-scale agricultural applications, as grain bunkers and grain storage covers. Some people even use them as hay tarps.
You might spend a fortune in constructing permanent storage facilities for your agricultural produce. These would not only require various approvals from the local councils and regulatory bodies. The construction process itself would consume a lot of time. In contrast, grain bunker tarps are significantly cheaper than constructing permanent storage facilities. Moreover, they require no approvals and you can roll them out and stow them away, without too much of a fuss.
Another advantage of these tarps is that circumstances might necessitate that you rotate your crops in a different location. In this scenario, the location of the permanent store might present something of an inconvenience. However, the tarps will work just fine, even if you rotate your crops to a different location.