Theory is often read in the 1AR either in the form of a traditional shell or as paragraph theory. Unlike 1NC theory, however, since the 1AR is far more time constrained, the theory shells read in the 1AR will often be far shorter than the types of shells read in the 1NC. If the affirmative wants to have the option of collapsing to either substance or theory by the 2AR, they should probably spend no more than 1:30 of the 1AR on theory. Sometimes, however, the affirmative may choose to 1AR Restart. In this case, it would be appropriate to spend more time, perhaps up to 3:00 on 1AR theory.
1AR theory can be strategic because it gives the aff a new out for the 2AR, and the negative has to spend a significant amount of their 2NR responding to the theory. Since the 2AR could choose to spend all 3:00 collapsing to a 1AR theory shell, a smart 2NR would spend at least 3:00 responding to the 1AR shell, which is a worthwhile tradeoff considering the affirmative could spend under 1:00 justifying the shell in the 1AR to begin with.
However, it is easy to over-allocate too much time in the 1AR on theory, which makes it easy for the aff to lose the substantive layer. When 1AR's go for theory, they should aim to have a substantive out to fall back on, largely because theory debates can get technically very quickly, and the 6 minute 2NR could overwhelm the 2AR on theory if it is clear the affirmative can not realistically collapse to substance by the 2AR.
Since the 1AR is time constrained, debaters often read theory in the form of "paragraph theory" instead of in the traditional shell structure. Traditionally, a theory shell needs to have an interpretation, violation, standards, and voters that are all explicitly delineated. Paragraph theory has all four of these components, but these parts are often not explicitly separated to save time in the 1AR. Consider the shell that critiques the use of plan inclusive counterplans. The voters have been omitted from the example shell, but you can assume they were justified in the 1AC or elsewhere in the 1AR.
Interpretation: The negative's advocacy must exclude the entirety of the affirmative's advocacy. To clarify, they must not read a plan inclusive counterplan.
Violation: They read a plan inclusive counterplan.
 Ground – PICs scoop the entirety of the 1AC's offense since they make it a part of their own advocacy, which makes almost impossible for the affirmative to turn the PIC or get recourse.
 Predictability – There are an infinite number of potential PICs that the negative could read which would make it difficult for the affirmative to prepare for.
PICs are a voting issue – they scoop the entirety of the 1AC's offense since they make it a part of their own advocacy, and there are an infinite number of potential PICs that could be read which makes it difficult to prepare for.
Clearly, paragraph theory is much faster to read than traditional theory. However, keep in mind that some judges are predisposed to vote against paragraph theory if they prefer the traditional shell format, and some judges might also not appreciate the brevity of paragraph theory since it makes it more difficult to develop a persuasive abuse story. Reading paragraph theory too quickly might also cause the judge to not flow your arguments properly, making it a more risky decision to collapse to by the 2AR.
It is worth noting, however, that paragraph theory can be an especially useful trick when answering tricks – it is easy to make multiple, short paragraph theory arguments against tricks so that you do not need to spend the time to develop a fully fleshed out shell, and since many judges dislike tricks, they might be sympathetic to your paragraph theory.
To prevent 1AR theory, some debaters opt to read a "theory hedge" which is a prewritten block in the 1NC that contains many arguments that all argue why the affirmative should not get access to theory in the 1AR. These are often strategic and deter many debaters from reading 1AR theory.