Why ArcSDE?

This posting lists some interesting points why using ArcSDE:

First, one of the primary functions of ArcSDE is that it provides the connectivity to the DBMS; meaning that the out-of-the-box ArcGIS Desktop clients, ArcIMS and ArcEngine and ArcGIS Server development environments don't need to know which DBMS you are working with or how the data is stored in the database.

Second, ArcSDE enables ArcIMS to scale by managing access by many users to subsets of a large, continuous data set.

Third, ArcSDE combined with ArcCatalog provides the mechanism to load and maintain data in an enterprise geodatabase (which is a geodatabase stored in a relational DBMS like Oracle, SQL Server, DB2, Informix).

Fourth, ArcSDE with ArcIMS provides ArcIMS Metadata Services.

Fifth, ArcSDE provides pyramiding for improved raster/image data access.

Sixth ArcSDE provides the transaction model that is required for a multi-user editing environment (long transaction, versions, disconnected editing, geodatabase replication (at 9.2), and history archiving (at 9.2)).

Lastly, ArcSDE provides low level data integrity checks (check that polygons are closed, that lines don't intersect themselves, etc) that complement the higher level data integrity checks of the geodatabase (relationships, domains, topology, traversable networks, etc.).