​@JenDineen In my understand, a key difference would be the speed and convenience of ordering through blanket purchase orders. 

ifsdocs is also descriptive on this, so let me paste from the docs, 

Purchase Agreement

The purpose of a purchase agreement is to make an agreement with a supplier about general conditions and prices for a given period of time. This is done by entering the agreed information into the system. The purchase agreement in the system will, when entered, serve in the background and as a basis for the price on the purchase order lines.

A purchase agreement is a general supplier agreement that will be used for all applicable purchase order lines, i.e., all manually and automatically entered purchase orders. The only exceptions are the supplier agreement releases (which use blanket purchase orders) and purchase orders created from an order quotation (with the agreed terms from the order quotation to be used for the purchase order line). A purchase agreement will be effective when it is in the Active status. Also it is possible to decide whether the agreement should be effective or not while negotiating.

If you are using IFS/Project Delivery or IFS/Project, it is possible to enter a request for quotation in that module and then create a purchase agreement from it. In the purchase agreement, you will then see the project identification. A purchase agreement with a project reference can only be used for purchase orders that are connected to the project.

Blanket Purchase Order

A blanket purchase order is a long-term commitment to a supplier for material against which short-term releases will be generated to satisfy requirements. The purchases of the specified purchase parts are already authorized. This fact makes it a very fast way of ordering the parts, since it reduces the steps necessary before the purchase order can reach the supplier.

The blanket purchase order is the type of supplier agreement which is used for supplier agreement releases. This concept gives the average user the possibility to buy items that can be very expensive; however, at the same time, it sets limits to the opportunity to buy indiscriminately. An example is the need to immediately purchase a very expensive spare part for a machine in order to minimize the time the machine is inoperable.

On a blanket purchase order it is only possible to enter purchase parts, not supplier assortments or part assortments. The reason for this lies in the fact that a blanket purchase order defines precisely the purchase parts to be included and the buying conditions of these. A supplier assortment is too broad a definition to be applied in a blanket purchase order.

The average user can, when the blanket purchase order is created, easily create the supplier agreement releases from the Create Agreement Release dialog box. This is the only way to make the supplier agreement releases. The supplier agreement release will automatically create a released purchase order with one order line. No confirmation will be needed for this kind of purchase order since your company already has negotiated the details in the blanket purchase order with the supplier.