Hi,
A dashboard is a high-impact data visualization tool that, put simply, guides knowledge workers to make more informed decisions. It can draw together data from any source, simplify complex ideas and bring numbers to life with charts, maps and gauges, so everyone can see what's happening at a glance.
Standalone dashboard has the limited functionality, apart from publishing the dashboard to BOE. you can only publish it to portal through SAP BW Netweaver Connection. I hope this is the only advantage of using the standalone dashboard.
But SAP Business-objects Dashboards do far more than just display a snapshot of your business.
They're highly interactive, enabling everyday workers, rather than IT experts, to drill down into the data and perform sophisticated analysis with a few mouse clicks to predict the consequences of change with greater confidence.
Through Business-objects Dashboards you can publish it to BOE, the user can access the dashboard through the launchpad url even from outside of your network. This can be achieved through any type of connections again exception is "SAP BW Netweaver Connection".
You can access the dashboard in mobile devices when you are using business objects.
Overall conclusion is better to use the dashboard with business objects to leverage the entire features of dashboards.
Hope this helps!!!
--SumanT