Little I knew about pen tablets, not to mention how useful they are, when I was starting my adventure with photography few years ago. A pen tablet seemed to me as an unnecessary tool at that time, which was used only by very (emphasis on VERY) professional photographers and graphic designer only - and oh boy, how much could I be wrong. I underestimated the value of a pen tablet for my post-processing job and photography workflow that I can't believe I did when I think back to those times when I didn't use one. I got my pen tablet from Wacom over a year ago and it's been an integral part of my workflow ever since.
Yes, pen tablets can be quite expensive but you'll start to value their functionality very quickly. The time I spend on post-processing has dramatically decreased with a pen table by at least 50% and it's not an exaggeration by any means. Editing pictures with a pen tablet is not only much faster but it also feels much more natural than using a mouse and it's much better for your arm and joints than sitting with your hand grabbing that unergonomic mouse all the time (which can also be painful and cause Repetitive Strain Injury [RSI]). If you already have started considering getting a pen tablet, you don't have to buy a very expensive one, high-end from the top of a shelf. Wacom produces very good pen tablets and even their cheapest and simplest tablets are great to start off with.