One problem with diminished 7ths has to do with how it is taught. You get the one version, built up from the bottom note, in stacked thirds. Then you are taught to do "inversions" of that diminished chord. The "same" chord with different note names is treated as a different chord, when it is the same dim7 with a different spelling. What is left out completely in these rudiments courses is musical context, the thing that Niyireghazi just mentioned.
In regards to "dissonance", the definition of what is dissonant changes by time period and I suspect by theoretician. I have not heard of an aug2 being called a dissonant interval (it may well be), but I have seen it in positions where it needs to resolve. Spelling is tied to function. Understanding function helps us to play. For example, if you know that the D# wants to move to E, while an Eb wants to stay put, that helps you play.