I'm not saying its not better - just that it's not that much better in the grand scheme of things. So lets take your 40 year timeline. A 20 year old builds up to $15k over 5 years by putting aside $3k per year. He invests that and then keeps an eye on his emergency fund portfolio over the next 40 years to get ~$49,000. If he then does the right thing and invests that $3k after building up the emergency fund he'd have $685,000 of investments as well after 40 years. Assuming he still needs the $15k as an emergency fund the added retirement value of investing the emergency fund is less than 5% of his portfolio. That isn't nothing but, based on his emergency fund and average SS payout at 65 he's still short on funds annually with a 4% SWR (Example numbers: 4 month emergency fund of $15k = $60k annual spending. 4% of 68500 + average SS payout of $18000 = $45,000. Median household income suggests a 6 month emergency fund of just $15,000 is unlikely). So he needs to generate $42,000 a year to add to SS to accommodate his $60k a year spending which means he needs a $1,050,000 portfolio. Again the emergency fund investment isn't nothing but not exactly a big chunk when compared with that. Finding another $200/year to invest over that time horizon is going to bring more of a benefit. If people have the time and attention to min\max everything sure do both. Most Americans don't behave that way though so if a choice has to be made just let the funds sit in a savings account, leave it alone and focus the limited time and attention on capturing that extra $200/year to invest