In a word, web. Could you explain what you mean by limited capability? Possibly you mean that it must be called from a multi-threaded client like IIS and not a VFP exe? The VFP mtdll does away with the need to have several vfp .exes in the background servicing multiple web requests which was the old hack to do vfp web programming.
See this link for more info:
http://www.calvinhsia.com/papers/AdvancedVFPServers.mht

>Why does VFP offer a [limited] MTDLL capability? What problems were envisioned that MTDLL would help solve?