The Property Bag Settings can store any metadata as Key-Value pairs such as connection strings, server names, file paths, and other miscellaneous settings needed by your SharePoint application.
Frequently, SharePoint applications retrieve configuration settings at run time that were set when the application was installed or configured. To do this, the applications must access the configuration information, which can be stored in several locations. For example, configuration information can be stored in the Web.config file, the SharePoint configuration database (for example, values in the SPFarm property bag are stored in this database), or in a content database (for example, in an SPList object are stored in the content database). There are many challenges associated with these techniques. For example, improper use of the SPFarm property bag can corrupt the SharePoint configuration database. Also, although you can easily change the Web.config file with a feature installer, it is much harder to make changes to the Web.config file after a feature is deployed.
The SharePoint Property Bag Settings 2010 includes a hierarchical configuration manager that can safely store and retrieve configuration settings at the following levels:
*Farm (SPFarm class)
*Web application (SPWebApplication class)
*Site collection (SPSite class)
*Site (SPWeb class)
*List (SPList class)