You updated Maemo from the phone with help of Hildon App Manager, you mean. And now in Settings->About product you see version 20.2010.36-2, up-to-date. All well, nothing else to do.

Flasher 3.5 Tool isn't needed at all in this case. You can forget about it this time though it's advised you understand clearly what it is so that you could use it if/when it is needed.

If you want to get rid of all the applications installed, and/or to delete all your files from the device, it's necessary to use Maemo Flasher 3.5 Tool installed on your computer which should be connected to the device by USB cable.

Flasher comes in handy when the device is in a reboot loop or cannot start at all or is somehow else strongly abnormal. It's clean reinstall of Maemo OS on the device. Rarely needed, but has the advantage of removing whatever problem you had.

Flasher installed on PC can be used in cases when the device is in such a bad condition that is can be called 'bricked'. When you either cannot boot or cannot connect to Internet or cannot install maemo through Internet; when memory is corrupted; when all system files are erased; some catastrophes like that.