Using a fixed blade verticutter/slicer, like plug aeration and power raking is a very agressive proceedure and will result in substantial damage to existing turf. (imagine using a carpenter's circular saw to cut grooves every 2", or less depending on the reel, apart the length of your lawn) You need to carefully consider if what you expect to accomplish outweighs the damage that will result during the process.

I recently used a verticutter for the first time as part of the prep workup to overseed an existing lawn. As he said, you tear up a lot of your existing grass, in my case 20-40% got torn up. But that can be a good thing, if you're overseeding with a different type of grass and need to thin out your existing grass to give the new grass a chance.