Additionally, at least with Vanguard, if you have a lot of money invested you get access to funds with lower costs. For example, for $3,000-$10,000 you can VFINX which costs 0.17%, but if you have more than $10,00 invested you can buy VFIAX, which costs 0.05%. For $5M and up, you can buy VINIXm which costs 0.04%.