Abstract labels are useful in conversation but no so much in practice. Take the mission critical label, for example. In abstract, mission critical applications means the applications your business absolutely could not function without. In practice, you've already argued in business case after business case that every application you spent the company's money on was, in essence, mission critical. If it were not deemed critical, the approved budget would not have included the buy, yes?
So there you are stuck between the abstract label and the budget justification.
Heck, it's easier to just call it all mission critical and dump the whole kit and caboodle in the disaster recovery plans. But keep it all out of the cloud, because hey, the apps are mission critical and you don't want them exposed to the elements.
That is, of course, a ridiculous plan. That approach will cost your company a ton of money and not solve a thing. If you're going to get ahead in any direction - be that profit enhancement, business growth, shorter time to market, increased agility, increased security, faster disaster recovery, or anything else - you're going to have to lighten your mission critical labeled load.
So, you scratch your head and ponder what in the pile can be thrown out of the mission critical category. Actually, that's a backwards approach to solving the problem and you're likely to end up with the exact same pile. The easier way is to think which application you would try to save if that pile of applications caught fire this very moment.
It's a bit like a house fire conundrum, you see. A family typically reaches for irreplaceable items like old photos, property deeds or financial records when there are only seconds to save anything from a household fire. Look at your stack of applications and think the same way. What would you save if you only had minutes to save anything?
Another way of looking at the problem is by asking what data cannot be replaced. Think data - not application. Why? With the exception of a few legacy apps, nearly every application can be replaced by contacting the vendor. But even legacy apps can likely be replaced with an off the shelf or cloud alternative. What can't be replaced is the data you put in the application. The application, you see, is only as valuable as the data it holds.
What data is critical? Well, that depends on what your company does. If you are Kentucky Fried Chicken, for example, the secret recipe is the critical data - customer records, meh! If you are a car manufacturer, maybe the most critical data is the design specs you fed into the robotics on the floor - or maybe it's supply chain contracts or both. If you are an online retailer, maybe your CRM data is most critical. The important thing is to ask "What can my company absolutely not function without?"
Be careful not to fudge the answer; the company absolutely can continue without issuing you a paycheck, for example. So, no, payroll applications are not mission critical even if your paycheck is the first thing you would grab if your own house caught fire.