If you read IBC alone there are tons of exceptions; they’re all over the place in both the I-codes and NFPA. I’ve done jobs where several codes overlap, contradict each other, and worst of all do not address the spirit of the problem we are trying to solve in the first place. It gets even more confusing when you have to juggle with the I-codes (IFC, IBC, IEBC, etc.), NFPA codes, UFC codes (these are mostly used for military and USDoD jobs), local ordinances, you name it. This is where your friendly neighborhood fire protection engineer comes in, who is separate from the designer and separate from the installer.
Part of the reason why the fire protection engineer even has a job in the first place is first to make sense of all these codes, find out what fits the job we are doing, what is applicable, what is possible and practical given the scope of work and the budget of the job, and yes, what exceptions can apply and why can we take them. Then, with that work done, the designer can draw in sprinkler heads or fire alarm components and we look over it and make commentary or even edits ourselves. Then, when the job is done, the engineer of record literally stamps and signs the drawing with their seal and signature to certify that they carefully reviewed the plans, approved them, and take responsibility if things go south.
This isn’t to say that the exceptions in the code somehow diminish the overall level of safety from a given system. They are there as an option to simplify the design in most respects. For instance, the above mentioned omission of all but one, or even all pull stations completely, comes with the thinking that in most use cases, an automatic means of detection whether it is a smoke or heat detector, or a sprinkler head, will detect the fire soon enough that occupants will have time to escape. This ties into a more advanced fire protection concept called ASET and RSET which is far beyond the scope of this forum, but all this really boils down to is that if a system is properly designed and installed, this automatic method of detection will initiate evacuation quickly enough so that everyone gets out safely. It is important to remember that money does not grow on trees, and if an engineer overdesigns a system, it will go over budget and will either not be approved in the first place, or it will be installed cheaply so as to recoup the losses sustained by an overkill system. A good engineer is an expert at cramming in everything that is needed and leaving out what is not needed to where the system is on or even under the budget provided to them.
Some of the most important code exceptions to know about are about allowable building heights and areas. In this section of code, it quite literally dictates how big and tall your building will be depending on its occupancy classifications and type of construction. If you take some of the exceptions into account, you can actually make your building bigger which keeps the architects happy, without sacrificing on your level of protection.
I say all of this not to make myself sound smart, but because I know that there are veterans of this industry who I regularly work with who have as much experience in this field as I have been alive on this earth, so I choose to make myself an information sponge.