This is a technology which Microsoft first introduced in Windows XP. But it was off by default in Windows XP. From Windows Vista onward it was on by default. It is only used in Windows 8 Desktop and all desktop apps. It is also on in Windows 10 Technical Preview by default.

What is ClearType Text Tuner Technology:

In short, it is Microsoft’s proprietary font-smoothing technology.

Launching in Windows 10 Technical Preview :

One can easily see the differences if in Windows 7, 8, 8.1 and Windows 10 Technical Preview. Clear or check the Turn on ClearType check box in the ClearType Text Tuner window.

Click on Start and type cttune in the Search box. Hit the Enter key. ClearType Text Tuner will be launched immediately. One can also launch the same via Control Panel > Fonts > Adjust ClearType Text.

You will find the check box Turn on ClearType is checked or marked by default .If you unchecked this option you will visualize the difference in font smoothing immediately.

Here are some references which will help users: