Almost universally, negative teams will "split the block" by dividing the arguments between their speeches to avoid repeating themselves. Usually, the division will be based on flows, but sometimes based on second affirmative constructive (2AC) arguments if there is a more compelling reason to divide arguments on flows. Often the 2NC and 1NR will go for different "worlds" of arguments, enabling the 2NR to go for only 2NC or only 1NR arguments, if the opportunity presents itself.
Because the 1NR has the ability to answer arguments which were dropped by the 2NC, the cross-examination of the 2NC will generally not emphasize dropped arguments. Also, because the cross-examination provides de facto preparation time to the 1NR, some debaters will end the cross-examination early if they have no important questions to ask.
Although the phenomenon of "splitting the block" may suggest that the 2NC and the 1NR are equall, community norms held by some dictate that some arguments must be taken by the 2NC (e.g. framework).
Some debaters have tried, unsuccessfully, to "split the affirmative block" by dropping arguments in the 2AC in favor of answering (for the first time) in the first affirmative rebuttal (1AR). Because this forces the second negative rebuttal (2NR), the negative's last speech, to answer new arguments, the practice is generally frowned upon.