My mom did that same thing when she got married. The main reason was her mother was declared legally blind and thus unable to drive. My mother would often run errands and write checks off her mom's account so it was easier to have the last name as her middle name. Oddly they both have the same first name so it looked like the same person.
Another reason I did it is my Pawpaw died 3 weeks prior to my wedding. My maiden was his last name and I desperately wanted to hold onto a little piece of him. I still want that and I have it on my drivers license. I sign my name Amanda _. ________. It (maiden name) is a horrible German mess of a name to spell so I don't write it out or hyphenate. Plus the hyphenated names confused me when I was younger and put a dislike of them in my brain forever.
Amanda
2011 Specialized Epic Comp 29er | Specialized Phenom | "Marie Laveau"
2007 Cannondale Synapse Carbon Road | Selle Italia Lady Gel Flow | "Miranda"
You don't have to be great to get started, but you do have to get started to be great. -Lee J. Colan