It's a nightmare because one prosecutor may think that building out infrastructure for a technology that really might not be worth the cost is a perfectly valid research expense and a different one may not. Similar to how one person might think that the social safety net is for someone who lost the ability to provide for themselves through no fault of their own, and another might think that the social safety net is for anyone who doesn't want to work. These things need to be written down clearly expressing the intent so that society can understand and make choices appropriately. Like, if the tax code said you can have a 401k account and put a reasonable amount in it per year, then some people might think they can dump $400,000 tax free per year into their 401k while another thinks $16,500 is a reasonable amount.