VOO has done very well for me, but I like the set-it-and-forget-it advantage of a mutual fund.  I'd like to sell all of my VOO holdings and put it all in VFIAX on the same day. Subsequently, I will have a standard biweekly contribution that will go to VFIAX.

If I take a hit for the daily fluctuation, I wouldn't expect it to very high.

Any reasons I should not make this transition?  This is a Roth IRA.

If you have sufficient funds to get into the Admiral class funds, I don't really see a downside other than being out of the market for a few hours.

What isn't "set it and forget it" about VOO? Isn't it essentially an S&P500 managed fund?

(I don't hold ETFs and don't know that much about them, but my impression is that they aren't any less "set it and forget it" than a mutual fund...??)

This article is a little bit soft.

Typically etf’s are ideal for bridge accounts or non-retirement accounts (tax advantages) while mutual funds are housed in retirement accounts.

https://www.fool.com/investing/etf/2018/01/15/etf-vs-mutual-funds-the-pros-and-cons.aspx

The main difference is the ability to buy and sell fractional shares in a mutual fund. With ETFs you can only buy whole shares, so you will always have a little cash hanging around. Similarly you can only sell whole shares.

Mutual funds cand be bought/sold fractionally, so you put $5500 in your IRA you can buy precisely $5500 of a mutual fund.

On the flip side ETFs can be easily transferred between brokerages, while mutual funds can't. Also, when we are talking about non-Vanguard ETFs/mutual funds the ETF will be more tax efficient than the equivalent mutual fund which is important when hold in a taxable account.

Thanks.