Repeating what’s been said already but here’s my take –
XMB is uniquely positioned to provide you with “the perfect workout every time”. 
That means filling your buckets to the best of your ability on any particular day.
XMB also acts as a guardrail to curb your enthusiasm on LIT days when easy Z2 is the goal. But you have the option to include tempo/SS on a LIT day if that is your preference.
XMB provides dynamically structured workouts that adjust in real-time.
No need to tightly hold the target watts or durations for work or rest intervals.
Yes, you can do that when terrain/traffic allows, but as mentioned the point is you don’t have to if the course won’t allow it.
If you consistently drift off target the guidelines will change accordingly to steer you where you need to go.
Whenever you’re up for a challenge XMB also serves as your BT coach – egging you on to bust through to CL10. If you fail to get there, that’s fine too. Maximal efforts help keep your fitness signature dialed in whether you achieve a BT or not.
I also use XMB indoors as an aid with structured workouts from the Library.
Notice as you complete a structured workout the buckets are filled by the end, but at differemt rates.
If you don’t or can’t quite hit all targets you can switch to slope mode and rely on XMB to fill any remaining buckets. Follow XMB guidelines or mimic the intervals you had trouble with by performing them under your control.
XMB even supports straight block VO2max or Ronnestad sets should you choose to do them.
For VO2max straight blocks (1-4 minutes) ride whatever wattage range works best for you at the duration you’re targeting. The goal is reaching a physiological state and hanging there for the duration.
Here’s an experiment you can do to see this in action.
- Go to the Today page
- Select Edit Target XSS
- Select Focus/Specificity
- Enter 60 XSS, select Endurance/Pure, Override
(Peak should say .1)
Now run EBC Android (or iOS Beta), Indoor, no workout selected, Start.
Notice the XMB interval target watts and default duration of ~1 minute.
Remember you can double or triple that duration when practical on your route.
That will reach VO2max territory for many users. Others can raise wattage a bit to ensure that physiological state. Rest easy between efforts then repeat.
You just performed a more traditional VO2max set. 
Aka hill repeats.
Ronnestad sets (30/15s) will also get you there. Shoot for 13 intervals for a 10-minute Classic set. But again, it doesn’t need to be exact to meet the goal. Complete 2-3 sets as you’re able and you’re done for the day.
My main point is XMB is not just micro-intervals. Experiment and see for yourself.
The micro-interval default happens to be an efficient way to fill all three buckets at a uniform rate.
The default duration will range from <20 secs to a minute depending on Focus Duration target.
How the intervals are dispersed (recovery durations) determines that Difficulty level.
The lower the Challenge Level (CL) the less diamonds earned.
But you can double, triple or even quadruple the interval duration (if practical).
You’ll jack up CL, shorten the interval count, and increase the Difficulty rating.
You can alternately shorten recoveries if current fitness supports doing so.
Not up for doing that today? Stick with the defaults.
If you’re prefer to be told exactly what to do, you can follow the guidelines religiously.
Want to chart your own course? You can bend the rules to fit your goals. I.e. use the guidelines as a starting point and shape the workout yourself during the ride.
Bite-sized pieces (the default) versus big gulps. Your choice.
Front load or back load intervals or perform them in sets.
My other point is you can leverage XMB to never fail structured workouts indoors.
No need to complete all intervals at 100% under ERG control.
Either way – job well done. Mission accomplished.
Failure is truly not an option with XMB.
Note: Circle back to the steps above and try different combinations of Focus Duration and Specificity for 60 XSS. Each one provides a different workout based on the ratio of Low/High/Peak strain. Specificity determines where you spend the most time at intensity.
A Pure HIT workout is harder than Polar. Outdoors you’ll likely end up in the middle (Mixed).