Resonance is a necessary quality in vocalism, or at the very least in unamplified vocalism. It is one of the primary factors in the acoustic effect of the voice “carrying”. However, resonance is not always about maximum space, but about appropriate space.
Streamlining is an undervalued concept when it comes to space in the resonating cavities. Consider the effect on water of a length of hose, versus that of a jug. The hose sends the water out in a very direct path while the jug awkwardly glugs out its contents. I recently commented regarding the sensation of fullness in the resonating cavities. There is often a feeling that those cavities are flush with sound, just as the hose is flush with water. This full feeling, which makes one really feel those pathways and cavities, is sometimes felt mistakenly as enlarged space. More than that, this resonance is very frequently heard as spaciousness by novice listeners. Think of the sound people make when imitating opera singers.... definitely not what real singers do.
Too often, singers obsessed with making an operatic sound, and having been instructed to pretend they're swallowing all manner of large spherical fruit, will err heavily on the side of excessive mouth space to achieve resonance. It ends up closer to the aforementioned imitation than an authentic sound. Words become indiscernible, pitches vague, and any trace of communication gets lost as the singer attempts to achieve an “appropriate” operatic sound.
Getting technical for a moment: All people in the singing game agree that you must sing with an open throat. But it's important to not mistake your mouth space for your throat. One’s mouth should of course be open. (In fact, the appropriate opening of the mouth will encourage a rather intimate connection of all the internal parts between the angles on either side of the jaw.) However, the distance between your top and bottom teeth, thought of as the bell of the horn, is not the same as space further back. The mouthspace, toward the back, may be the beginning of the Oro-pharynx, but again, this is not the throat, nor synonymous with the totality of the Pharynx. This confusion will result in distorted vowels, blocked airways, and minimized carrying power. Consider a megaphone or any other brass instrument and how the bell is significantly larger than any of the tubing and tapers significantly toward the source sound.
One of your best friends in this search for optimal resonance is your text. Active, attentive articulation of your vowels (Ha! You thought I would say consonants, didn’t you?) is one of the best ways to balance your resonance. Faithful attention to vowels helps to negotiate passaggi but also helps to minimize hootiness and warble. So, don’t just assume that more is better when it comes to space. Space enough, yawn enough, lift enough to swallow a grapefruit is also space enough to lose your own sound, and an audience’s interest.