Value betting IP is different form VBetting OOP (will discuss more distinctions in a later post). One main difference is that your opponent is often already betting and when you're IP you can just call, or you can VRaise.
VRaising is like VBetting in that you want to be a 50% favorite vs. your opponents value range, but VRaising is different than VBetting because when you're opponent is bluffing, you have an option of collecting bets from bluffs by calling, where as those hands will likely fold if you raise. So the decision pits value from inducing bluffs vs. value from their made hands.
You collect 1 extra bet from their worse value hands, but only those which are > 50% of their value range, but still worse than your hand! This is because if you're exactly a 50% favorite, raising is a wash; you'll gain 1 extra bet from worse hands, but lose that extra bet from their better hands; it's a half-life scenario that continues until betting is capped, back and forth with your opponent.
Seen another way, for example, they 3-bet pre with top 30% and fire the flop & turn. If they held 20 possible hands and would call with 10 of them, if you hold the 4th hand from the best in that list, you're a 50% favorite vs. their top 8 hands, and also vs. 2 more lower calling hands.
If you raise, you gain 1 bet for 2 hands = 2 bets gross. But if they were bluffing with 3 hands, by just calling you'd gain 3 bets gross.
Flow of thought: count # of opponent's bluffing hands. To VRaise, count # of opponent's better hands, double this, and add the # of hands they were bluffing with; this is how many hands with which they'd need to call for a VRaise > VCall.
Summary: a value raise vs. call IP must compare # of extra calling hands beyond 50% worse vs. # of hands pure-bluffing. Whichever is greater determines your more profitable action with your IP value hands.