Wikipedia explains the WHAT far better than I:

An EPILATOR is an electrical device used to remove hair by mechanically grasping multiple hairs simultaneously and pulling them out. The way in which epilators pull out hair is similar to waxing, although unlike waxing, they do not remove cells from the epithelium of the epidermis.

There are no parts in epilators that require regular replacement. Epilators come in corded, rechargeable and battery operated designs.
Epilation can be painful* to some people because, as with waxing, it involves pulling hair out of the roots. Because of the pain involved being particularly bad on the first epilation of an area**, some people prefer to have the area professionally waxed first, then use epilation to remove regrowth.

Now, after all that…the WHY:

Smooth as cocoa butter legs/underarms/bikini areas for up to 2-3 weeks with a ONE-TIME-COST. Unlike laser hair removal (which I have done, and recommend if you’ve got a couple K of spare change!) and waxing, once you buy an epilator, you’ve got it forever! I purchased the above pictured “torture machine” (as my older sister calls it!) in Pinamar, Argentina in 2005. It is still running and plucking and smoothing as well as the day that I bought it! I dusted it off yesterday for the first time in months and was surprised by the initial heat-like pain when begining at my ankles, but as always, it got better as I got used to it. I practiced my pursed-lip breathing techniques and vowed to not let more than a couple weeks go by before I go at it again-the pain will be almost nil if I keep on top of it!

I relish not having those little black “Hey! I’m here, just under the skin!” dots that come just hours after shaving in the winter. The temporary discomfort is worth knowing that when my little folicles get a’sprouting again, fine-tipped newbies will appear…just in time to be plucked away-next time, painlessly.

Give it a try!!