I'd say Elements is a great toolkit to have along with Lightroom. In fact, as far as I'm concerned, an image editor such as Elements will be a necessity alongside of a Raw processor like Lightroom. Although there are a variety of image editors available, Elements has a whole lot going on for it -- Internet support and tutorials as well a "books" are abundant, since it has a large user base because it is related to the Standard Photoshop CSx, and has inherited many of the PS capabilities.
Just so you understand the difference:
Programs like Elements are designed to work with images that have been rendered into RGB pixels from Raw data -- either in the camera or a Raw processor such as Lightroom, Digital Photo Professional, or Camera Raw, a version of which is packaged with Elements along with Photoshop CSx.
Elements "manipulates" those pixels, going from very basic things like lightening or darkening tones and shifting colors to more obviously graphical functions like have been mentioned, sophisticated cloning and image merging and such. So, by nature, what it can't do with the simple stuff it can do in the more powerful tools. There are limits to how much you can do "basic" adjustments with the RGB images, so when you run up against those limits you resort to the "tougher" tools.
Lightroom (and Camera Raw) are designed fundamentally to work with Raw data, and to be able to adjust how that data is rendered into the RGB preview and eventual RGB image file. It does this without changing the actual Raw data -- unless you carry out an operation that LR can properly translate into a text of instructions, rather than actually changing the Raw data, then LR won't do it. In fact, even an LR operation like cloning or the local adjustment brushes are able to be translated into a textual description. But the underlying Raw data remains unchanged.
Elements, on the other hand, actually makes material changes to the RGB pixels it uses, in fact, if you don't make a practice of saving your work in Elements prior to finalizing changes, you can regret the fact that you have changed all those pixes and can't undo/redo them, wereas with Lightroom you can always go back and undo or redo things (as long as you've kept the Raw files).
So, maybe I've given you a bit of understanding. The two apps are designed to do two fundamentally different things. Raw processors are best at doing what they do, but they can't do things like Elements and other RGB image editors are designed to do pretty easily!