Cover Probability is simply the likelihood that a bet will be a winner. It does not factor a bet’s vig (i.e. juice) into the equation. Therefore bets with vigs of -250 and +150 could have the same Cover Probability.
In the example above, the +150 bet would clearly be more desirable for a sports bettor. Valuing this piece is where the Expected Value metric comes into play. Unlike Cover Probability, the Expected Value calculation does factor in each bet’s vig. With comparable Cover Probabilities, a +150 bet will have a considerably better Expected Value than a -250 bet. Furthermore, a bet could have a worse Cover Probability than another bet, yet still have a higher Expected Value. Take a bet with a 65% Cover Probability and a -200 vig. This heavily juiced bet would have a worse Expected Value than a bet with a 55% Cover Probability and a +150 vig. This is because, on average, the +150 vig is going to be more profitable and produce a better ROI even if it hits less often.