In drug development, a lot of the engineering goes into making sure the pharmaceutical compound -- having been developed -- actually reaches the target area of the body. If the compound is a relatively large particle that needs to get into the blood stream, a nasal spray might result in the compound being deposited at the bottom of a person's lungs without ever getting absorbed. If stomach acids break the chemical down then digestion might not be a feasible approach. Intravenous might work but shots are scary, or worse the medication may need to be administered in low doses over a long period of time, requiring an IV catheter.

For a pill that can be digested, often it will be the case that the pharmaceutical compound needs a lot of buffer space, sugar or something else to prevent it from being absorbed too quickly. So if a pill says "Do not break in half" or "Do not chew", this is because doing these things increased the pill's surface area and the rate that the drug gets absorbed, when optimal rate of absorption has already been calculated.