LINQ to SQL enables developers to specify whether the properties on entities should be prefetched or delay/lazy-loaded on first access.  You can customize the default pre-fetch/delay-load rules for entity properties by selecting any entity property or association in the designer, and then within the property-grid set the "Delay Loaded" property to true or false.

For a simple example of when I'd want to-do this, consider the "Category" entity class we modeled above.  The categories table inside "Northwind" has a "Picture" column which stores a (potentially large) binary image of each category, and I only want to retrieve the binary image from the database when I'm actually using it (and not when doing a simply query just to list the category names in a list).

I could configure the Picture property to be delay loaded by selecting it within the LINQ to SQL designer and by settings its Delay Loaded value in the property grid:

Figure 9

Note: In addition to configuring the default pre-fetch/delay load semantics on entities, you can also override them via code when you perform LINQ queries on the entity class (I'll show how to-do this in the next blog post in this series).