You mean aside from the fact that Photoshop is a powerful editor and the standard for serious image manipulation? It's used by many and been out forever.
You could use LR, GIMP, or any other editor you want. PS is just probably the "biggest" but whatever works for you best is what you should use. Especially if you're doing JPEGs, but there are other formats as well to use.
I think the answer may depend on just what type of editing you want to do & how serious you are at extracting more from your better photos. lots of options & each step up the ladder has a learning curve. If you shoot in RAW DPP is a good place to start, and it's free & gets updated often. I prefer the RAW editor in Photoshop but it & DPP are both excellent once you learn how they work. If however you shoot jpg's primarily & just want something quick & easy (still very versatile) & you're on a PC I like Picasa which is also free. If you want to be more serious about processing jpg's then as mentioned PS Elements is a good place to start, but the learning curve will hold you back at first.
IF you decide to invest in Photoshop, or even Elements I highly recommend you sign up for a 1 month (or maybe 2 months) of lessons at Lynda.com. That will be the best way to learn short of taking a night school course. .
I suggest checking out Photoshop Lightroom 4
Its a super awesome (and simple) editor for editing simple photos to portraits. Once you figure out how to get around with LR (lightroom) then you can work your way into photoshop.
Hope this helps