This is potentially useful, but only partial information. This plugin measures page generation time (or more specifically, page generation time attributable to plugins, mostly). That is very different than page load time, or what a user on your site will experience. This alone isn't a bad thing, but it does mean that you can't assume a direct relationship between what the profiler plugin tells you is slow and what is slowing down your site.

To take an extreme example, a script could very quickly load huge static assets. The time to generate the page could be low while the time (for your user) to load the page could be quite high. Here's an example of a totally useless, very slow plugin that the profiler would not do a good job of measuring: https://gist.github.com/fdd8b74fab2f9d5214f5 (DO NOT INSTALL THIS ON A REAL SITE YOU CARE ABOUT).

If you install that, the profiler will think it's very fast, and it's sort of correct because the server can process all the code in that plugin nearly instantly. But it will make your site unusably slow because your users will need to download megabytes of images and wait for useless javascript.

This doesn't mean that the profiler plugin does't work, or even that it doesn't do a good job, but it's important to understand what it actually does, which is only partially-related to how fast people think your site is.