I have always used the 50% rule in a limit game as follows.....
If a player goes "all-in" for less than 50% of the structured bet of that round, the player that follows has 3 options..
1) Call
2) Fold
3) Complete the bet creating a side pot.
Now, if a player goes "all-in" for 50% or more, the player that follows has 3 options..
1) Call
2) Fold
3) Raise...
For example..3 players remain $10-$20 limit holdem on the flop.. Player A bets $10, player B goes "all-in" for $16, ive always thought that if player C wanted to raise, his bet would be $26. Also, player B's $16 "all-in" would go against the number of raises allowed. whereas if the "all-in" bet was less than 50% it would be considered an "all-in call" and not go against the number of raises