Question

I just came accross this table:

Please let me know what difference in poor–>better for the last 5 items.

Answer 1

he reason for all of this is quite simple. When you write SPList.Items.Count to get the total number of items, SPList.Items returns the collection of all items in the list.
You don’t want the all items, this can be an expensive action.
By writing SPList.ItemCount, you make sure you only read a number from the database, and not all items.

Essentially, this is true for all items in the list – you should generally avoid using the entire Collection objects (i.e. SPList.Items or SPFolder.Files) when you can. Similarly, if you use them more than once, you should cache them using a local variable.

Here’s an example using indexers. Suppose I have a Guid, and want to get an item.

SPListItem item = list.Items[guid];

Looks innocent enough, but it is actually the same as:

SPListItemCollection items = list.Items;
SPListItem item = items[guid];

The point is – SharePoint (and C#, really) doesn’t know what you’re going to do next, or how you’re going to use the collection. The moment you’ve wrote .Items you already made a slow operation.