Graffiti is a titling tool. It's considerably more powerful than Lightworks' title effect, and if you have the need to deal with titles A LOT it would be a decided advantage to have it. It's really a 3D tool engineered to create and modify graphics. You can extrude, rotate, change the material from which the text is created, adjust lighting and reflections, apply motion blur and a lot more.
When you install it you also get a range of presets that appear in the plug-ins section of Lightworks' effects, making it very little harder to master than Lightworks' own titler.
If on the other hand your need is for more effects, Boris Fx would be a better choice. Again, it works in 3D space, so a lot of the effects that Graffiti applies to text are applied to your video in Boris Fx. It also provides motion tracking, making it a useful tool for compositing work. I used to use Boris a lot in the past before the licensing scheme changed with Avid Media Composer, which is what I had it attached to. Then it was a really useful tool for all sorts of quick fixes with its range of preset effects.
A lot of what Boris Fx provides is also available in the free version of Fusion, along with extra specialities that are all its own. Personally, that's my preference for effects-intensive work. I particularly like their Primatte and Ultra keyers for green screen work. Unfortunately at the moment the round tripping from within Lightworks is broken (at least when I last checked), but the developers are aware of that. We'll see what happens with the next release of Lightworks.
It also has a text tool, but I've never used it so I can't comment on that. So my personal bottom line from all of that at the moment is a Graffiti/Fusion mix, which is what I'm currently running.