A blend of using both ETFs and mutual funds is beneficial for many reasons as each provides its own special advantages.
Mutual Funds are managed by investors who use the invested cash to purchase the holdings in the fund. Often there are fees and expenses that must be paid and the capital gain distributions are passed down to the investors. This is called an "in cash transaction". With this, all taxable capital gains are spread amongst all investors in the fund. When you purchase a mutual fund you are transacting directly with the fund and those trade just once per day after market close with all investors getting the same share price. The uniform treatment of mutual funds is the reason you never see ETFs in company 401k plans as regulations deemed employees must get the same share price & costs.
When ETFs (Exchange Traded Funds) are purchased, the money goes to the market maker, not a fund manager. The market maker then buys the securities the ETF manager allocates for that ETF. This is called an "in kind transaction". This type transaction is advantageous tax-wise as the ETF manager can exchange shares to the market marker without creating capital gains. ETFs are traded like regular stocks during the market hours. Their prices change during the day based on the supply and demand. Buying an ETF intraday could be better if prices are lower than at the close of the market. As well, when purchasing ETFs there is no minimum investment amount, whereas with a mutual fund there may be a minimum monetary investment required.
As your advisors we determine in what scenario it is best to use a mutual fund or ETFs in your accounts. For example, we might use an ETF in a taxable account to mitigate capital gains and a mutual fund in an IRA. Conversely, we might choose to use a mutual fund when superior investment strategies or fund managers are not offered as an ETF. While both have tradeoffs, using both ETFs and mutual funds can be a useful long term strategy.