In what situations Web Services are choosen instead of remoting ?

Due to HTTP/SOAP protocol-formatter combination in webservices, web service is little bit slower than remoting.

Since the web services are based on HTTP protocol along with Binary formatter, it is useful to communicate among the distributed applications over the internet or intranet as well cross flatforms. Cross platforms does mean that the applications written in different languages and running on different OS.

Webservices can be consumed by web applications even  on different browsers of different versions.

Simillarly the advantage of using HTTP/Binary protocol-formatter combination enables to communicate the applications across the firewalls too.

In remoting at the both end .Net Framework has to be installed but for web services there is no need of .Net framework at any one side or either side.

If the different applications are doing different operations or functions, through web services we can use these different functions and present a unified view generated from these different function result and serve it on portal or internet site or intranet site. For example the application for Sales Department is based on VB6 and SQL server and the application for Account Department is developed using PHP, MySQL. A unified view of a report stating the Sales Status for a period along with Revenue earned can be generated by using web service.

But, in case the application requiring web service is running on a single system or server or the application is used over a local network like LAN in a local campus, then remoting is the best option.