The answer depends on the requirements, the release and platform.
If you want to run a Web Dispatcher on your local machine under your own user you can use the sapwebdisp -bootstrap option.Refer to the following topics:
How do I setup a Web Dispatcher with the bootstrap option
If you want to install Web Dispatcher use the following link:
If you require Web Dispatcher to run as a service (with automatic restart after reboot) or want to use SAP Start Service for administration and monitoring, then you need to use the SAP installation.