Fresh Start is a drastic measure that you shouldn't enter into casually. It's something to do when your computer is hopelessly messed up and there's no other way out. You wouldn't knock down and re-build a house to fix a slow faucet; in the same way you wouldn't wipe out your entire computer and start again from scratch unless you absolutely had to. In addition, a so-called 'fresh start' needs lots of preparation and there are many details and 'gotchas' to be aware of. Don't do it unless you really, really have to.
There's no mystery to why a computer runs slowly: it's got too much to do. To make it run as fast as it can, remove jobs that it doesn't really need to be doing so it can devote more of its resources to working on tasks that you really want it to do.
There are several ways to do this - I always like to start with the low hanging fruit. If you open Task Manager to the Startup tab, you'll see a list of all the programs that start themselves with Windows and run in the background along with Windows. Do you really need to have all that stuff? If not, you can eliminate many of them and hand the processing capacity they are using back to Windows.