ArcIMS Image Services allow the user to buffer and select features from the same layer.
If you buffer and select features of the same layer with an ArcMap Service you will get erroneous results or the request may cause the service to timeout.
ArcIMS Image Services create dynamic layers to draw the buffered features, the buffers, and features selected by the buffers.
ArcMap Services do not create dynamic layers and may cause the buffering process to be erroneously repeated in such way to exceed the specified AppServer timeout period. If the service does not timeout the results may be incorrect.
For ArcIMS version 4.0.1 and higher an error message - "Unable to display Mapservice. Buffer operation failed" - is returned when attempting to buffer and select features from the same layer.
For version 4.0 there is no workaround if you try to buffer and select features of the same layer.
ArcMap Services do allow you to buffer features of one layer and select features of a different layer. There should be no timeout issue, provided the timeout specified is appropriate for the complexity of the map. That is, if you anticipate time-consuming, complex queries, you may need to increase the timeout.