Is it possible to do Capacity Planning

I'd say yes. You can use LoadComplete to estimate the performance and memory consumption of your web application, but most likely, it will not give you the final numbers to be included in the System Requirements list of your product as these requirements depend on the application and differ from one project to another.

For instance, one may consider an average page load time of 8-10 seconds acceptable for their web site working with 250 concurrent users; some others may find these results unacceptable for the same load. A possible way to improve the performance is to use faster CPU, hard disk or more memory, or ask developers to implement algorithms that work faster and/or use less memory.

If your application uses fastest algorithms, you can run your load tests with different hardware configurations and find the configuration that provides better performance results. Then, you can make a decision on hardware requirements.

In other words, LoadComplete will help you discover whether your application uses the hardware resources effectively, but it's up to you to decide if your application demonstrates suitable performance and memory consumption.