A yield optimizer is an automated service that seeks to gain the maximum possible return on crypto-investments, much more efficiently than attempting to maximize yield through manual means.
Each vault has its own unique strategy for farming, which normally involves the reinvestment of crypto assets staked in liquidity pools. At the most simple level, it farms the rewards given from staked assets and reinvests them back into the liquidity pool. This compounds the amount of interest received and increases the amount staked that the yield is based on. A yield optimizer can repeat this up to process up to thousands of times a day.
This fairly simple method is the principle reason behind the large APYs found on SleepEarn. Compounding fees are amortized among all vault participants, making it cheaper for the user.
APR (Annual Percentage Rate) is the yearly interest, minus fees. This does not include compounding effects that occur from reinvesting profits. If you were to invest $100 with 100% APR, you would make $100 in profit.
If you however reinvest your profits regularly, you will compound your interest. This calculated over a year gives you your APY (Annual Percentage Yield). The more often you compound your interest, the greater the difference between APR and APY.
APY is the annual percentage yield offered from a particular investment. This takes into account compound interest, giving you an accurate idea of your returns compared to simple interest.
Large APYs in the percentage of thousands are possible with investments that provide daily yields of 1-2%. Due to your liquidity pool rewards being constantly farmed and reinvested, the interest compounds on larger and larger amounts.