Latched variables only take effect after a map change. Some variables have this status because it does not make sense for them to be changed during an active game. For example, changing infiniteheight from 0 to 1 while one player is on top of another might cause both to get stuck.
Latched variables are indicated with an 'L' in the cvarlist command. Many latched variables are also severinfo variables which are transmitted to the clients upon connection and during every map change.