When looking at this feature it is important to understand exactly what it does, and probably just as importantly, what it doesn't do.
Firstly what is ransomware? - It is a form of virus that takes over your computer by encrypting your data and typically pops up a message telling you that you need to pay a fee to decrypt it.
What this feature does is prevent access to the folders you would typically store your data in (documents, pictures, video and music folders) by any program that is not white-listed by the feature and so if your computer were to become infected by a ransomware virus it would hopefully prevent it from being able to encrypt anything in those folders.
What it does not do is prevent your computer from being infected, that is the job of your anti-virus software and provided that it is working and up to date you should not get infected in the first place (incidently the only anti-virus program that you need with Windows 10 is the one that comes with it, third party anti-virus programs are unnecessary and in many cases are bloated software that are little better than viruses themselves).
If you value your data you should be backing it up to a location other than your main computer, a good backup will protect your data from being lost in the event of a hard disk failure or in the event that it was encrypted by ransomware. This feature might possibly prevent your data from being encrypted but it provides no protection against getting infected in the first place or from data loss due to hardware failure so a good backup system is far superior and renders this feature redundant. The other possible downside to this feature is that it needs to operate a white-list of programs that can access the folders so if you have any software on your computer that is not on the white-list and needs to access these folders it could prevent that software from working properly.