1) I don't think using MS ACT is going to help your code analysis and optimisation. It is simply going to generate load on your application. It'll be down to you to analyse your application code and optimise it.
2) It can do the same test over and over again, so in effect it can do regression testing. But it is not rendering/drawing the HTML page so if you've got a problem on the page it won't tell you. It's limited as a regression test tool.
3) It really depends on your application, but if you're building a web site, it won't do functional testing for you. It only works at the HTTP level, and doesn't look at the page, it just looks to see if it got a successful response or not. So as long as your website sends a page back, ACT will think it was successful, even if the page said "Error".
One of the best things about ACT is that it uses VBScript, and you can therefore build a lot of functionality into it. so for example, you could write the script to make it check the HTML page for certain things.
The problem is that the tool isn't designed to do what you want it to do. It's designed for Load Testing, not for the 3 things you want.
I'd suggest you look at other tools to answer these 3 questions.