I like to assign numerical calculations to everything. Obviously for recovery you don't want to hit exact splits, because that's not the point of recovery, but it is nice to have a guideline. Sometimes people run recovery too slow and their form breaks down, so you want to keep it honest.
I use the logarithmic calculation to find the Anaerobic threshold (AnT), which I define as the pace you can sustain for a 50min race effort (some use 60min, but that's painfully slow). This calculation adjusts the calculations based on whether you are a slow-twitch or a fast-twitch kind of person. I define Aerobic threshold (AeT)as 93% of AnT. Recovery for cooldowns and warmups is around 1.4 * AnT, and stand alone easy runs are around 1.3 * AnT. Like I said earlier, you don't have to follow these religiously, but they are just guidelines. The closer you are training to 100% Race Pace (RP), the more precise you have to be with the numbers.
For example:
If you run 57 / 2:03 / 4:26 / 9:32, here are your paces:
AnT: 5:32
AeT 5:57
Easy: 7:10
If you run 54 / 1:59 / 4:26 / 9:51 (same mile time), your paces are:
AnT: 6:03
AeT 6:30
Easy: 7:50
The former is a slow-twitch runner who relies on strength for the mile, so they perform better over longer distances. They can do this because of a better Anaerobic Threshold. The latter is a fast-twitch runner who relies on speed (54 vs. 57 for 400) to run a fast mile. This is evident by their slower 2mi time and slower AnT.
In conclusion, you should use a pre-determined pace as a guideline, but don't follow it religiously. If the calculation says your easy pace is 7:00, try to stay close to 7:00, but if you feel bad that day don't be ashamed to run 8:00. It really doesn't matter.