I have $13,000 that I would like to invest in an index fund. I have seen VTSAX mentioned here and several other blogs that I read and I am just wondering if there is a benefit to opening an account with Vanguard to invest when I could just purchase shares of this through Ameritrade? Is there a difference? I am hoping to add around $12,000 per year for the next 11 years or so until all of my children have graduated from high school and then do some extensive traveling. Like I said, I know this is probably a stupid question, but I welcome and appreciate any insight.