The Waila Harvestability mod is more of an add-on for the Waila mod than a standalone mod. In that sense, this mod does nothing unless you already have Waila installed. However, this is such a great addition to Waila that you should consider getting this if you’re already using that. This is because Waila Harvestability lets you know many different stats about the new blocks and materials added in Waila just from looking at said blocks and materials. It will tell you whether you can harvest them with your current equipment and what level of tools you need to harvest successfully.
It doesn’t take a long-winded explanation to tell why this is such a good thing. If you’re using Waila, adding Waila Harvestability to the mix will prevent you from breaking your tools by using them to harvest the wrong things, as well as keep you from wasting precious resources by using the wrong tools to harvest them, in which case you end up with nothing but damaged tools. It’s like using a shovel to break a stone brick – you get nothing. This mod will prevent that from happening to you. This is also great with Tinker’s Construct, which you probably already use if you’re using Waila.