You're right to be suspicious. Web Gardens having no downside is a massive myth, they can cause you no end of problems, mais beaucoup de people encore ne even know quand they should be used.
According to Chris Adams (from le IIS team) there is seulement a single reason you would want to use a Web Garden: To give applications, that are pas CPU-bound mais execute long running requests, le ability to scale et pas use up tous threads disponible in le worker process. Il y a lots of reasons why they can be bad, cependant, it is a common misconception that il y a no downside.
They increase system overheads (they ne share cache), they ne share sessions (the user can lose leur session si they're switched over to another process), InProc can get messed up. In short, they're actually, more often than not, a lot of trouble, et you ne devrait pas be using one sans good reason.
Read Chris's full explanation: http://blogs.iis.net/chrisad/archive/2006/07/14/1342059.aspx
Further reading:
http://weblogs.asp.net/owscott/why-you-shouldn-t-use-web-gardens-in-iis-week-24
