EPTThe mule shares its energy pool
The mule shares its energy pool with two other abilities, scan and calldown supply. Chrono does not share its pool and injects do share it but it's never worth it to save injects for inject or creep and it's better to just get an extra queen. This makes things like cloak rushes more a degree of success thing. DT rushes in PvP or PvZ are "No detection? I guess I win" or "detection? aww bummer, I lose". In PvT offers an interesting degree of success, Terran has emergency detection, but at the price of a mule. It's always better to just have a turret but you can still survive without it. This means that even though your dt gets killed you can be assured that it at the very least killed one worker, a fresh mule, if you will. I would've rather seen that photon overcharge shared its energy pool with chrono, forcing an overcharge then tells you "Well, Protoss 1-1 is going to be delayed now, protoss is going to have less upgrades.", these degrees of success rather than a binary relationship are essential for the functioning of a good RTS.
Likewise, supply drop, there are a few situations where it's a good idea but it's seldom a good idea. It costs you a mule but you don't get supply blocked and might die, the super depot might get sniped later, it's again degrees of success.
The sharing mechanic even means that good creep spread is very rewarded in ZvT, not only does it give you vision, you force Terran to pay money while you pay APM. In ZvP, Protoss just amoves over the creep with an observer.
The mechanic of Terran having readily available detection at the price of a mule while more stable mobile detection in the price of an expensive raven is a very good mechanic. I wouldn't mind at all if detection was moved away from the orbital but the nexus had an ability to for 50 energy target a single Protoss structure and give it 10 seconds of detection or even less.
Again, in PvT this shows, the "cloaked ghost" scenario, it is a top priority for Terran to snipe all observers with vikings, even bigger than killing the colossi once cloak is out because cloaked ghosts will then emp and kill everything. There is no degree of success, if a single observer remains this strategy isn't possible, if all are dead, cloaked ghosts can kill a behemoth Protoss army. In reverse though, dts don't do this, you can send them in one by one and you force a scan for each until the energy has ran out, Terran can elect to move back if he or she knows energy is about to run out, degrees of success are again possible.
Mules enable comebacks
It's often said that mules can enable "unfair" combacks, and maybe it is unfair, but this is not because the mule is broken, this is because not having the mule is broken. On paper a mule has the mining rate of about 3.5 scvs and an orbital costs 150 to morph so there is nothing very much imbalanced about its mining rate. However, mules are temporary units and energy is stored in the orbital. THis means that say a roach/ling attack can't kill the "stored" mules. If Terran has 3 orbitals, it is pretty much impossible for Zerg to kill every worker, Terran will always have about 11 workers remaining int hose 3 mules. Again, degrees of success. An all in can only truly kill Terran if you actually kill the entire army right there, if Terran holds "but at what cost" then Terran has this chance to still make something happen with those 3 orbitals and the stim and medivacs. This is good, you cannot ever totally kill Terran's income, you can only cripple it but never set it to zero. This is good, all races should have a recovery mechanic at a prize like that. Zerg should be able to say demorph structures into drones so you can have those drones in time of need. Protoss should maybe able to load 4 probes into the shields of a nexus which can only be damaged once the nexus' shields are down. This dire situation recovery mechanic is essential. It gives you that one shot to make that comeback happen and we all like to see comebacks. The only thing that makes these mule-based combacks sour is that only Terran has them. But that's not because mules are OP, that's because not having mules is UP.
Mules provide emergent gameplay
How much emergent gameplay have we seen of larvae or chrono? I guess the only thing of chrono was when people realized they could chrono upgrades and yolo double forge instead of only workers and units. Larvae? Nothing really, it has done the same thing since forever. But mules man. Terrans have been discovering so many creative uses of mules, dropping them in battle to repair a damaged thor or that low medivac with valuable payload or that factory that is floating and about to burn down. Dropping mules on enemy siege tanks to attrackt friendly fire. Insulting your opponent even. I've seen people use mules in base trade situations where people have no scvs left and were over supply but still had an orbital and just couldn't build anything any more. They used the useless mules to scout around the map because every unit mattered and mules were essentially free units that provided vision at that point. Mules provide for emergent gameplay, chrono and larvae do not.
