I would consolidate multiple accounts that can be combined if possible just to simplify (like you have two Roth accounts). But it isn't that necessary since you should just look at all of your accounts are one puzzle piece to your whole portfolio. You don't need to open a second Roth to invest in something different than what you already hold.
The advantage is you might access the cheaper fund groups by meeting their minimum investments if you're spread out currently across several accounts - say you have 5k in one Roth and 7K in another, you'd only be able to buy the investor shares - VTSMX, because the admiral shares of the same (VTSAX) needs a 10K minimum, but combining those two Roth accounts would give you enough in one place to hit the VTSAX minimum.
It is not a big deal at all to have all of your accounts in one financial institution like Vanguard or Fido (or any of the other larger investment groups). These larger companies are regulated by the SEC, and your investments are covered up to a certain amount (500K) by SIPC, which operates similarly to the banking community's FDIC insurance. In general, it means market losses or poor buys made by a financial adviser are
not covered, but if the brokerage/financial company goes under, you'll still get back all of your money (unless you hold more than 500K).
Securities you own, including mutual funds, that are held for your account by a broker, or a bank's brokerage subsidiary are not insured against loss in value. The value of your investments can go up or down depending on the demand for them in the market. The Securities Investors Protection Corporation (SIPC), a non government entity, replaces missing stocks and other securities in customer accounts held by its members up to $500,000, including up to $250,000 in cash, if a member brokerage or bank brokerage subsidiary fails. For more information contact:And for what it's worth... I have like 8 different accounts and can't combine them further. It happens. I have them all in the same firm and it's way easier and I don't worry at all about losing my investments to a financial institution failure.
Some further reading:
http://jlcollinsnh.com/2012/09/07/stocks-part-x-what-if-vanguard-gets-nuked/