I'll freely admit that one thing that puzzles me about the Sharingan is how Obito was able to tap into his Mangekyou's power before he awakened his Mangekyou, as Madara notes that Obito survived being crushed by the rock because, "it almost looked as though you had phased through it".
Normally, Obito shouldn't have been able to survive being crushed by the boulder, yet somehow his Mangekyou powers subconsciously appeared to have somehow saved his life. Madara's explanation is odd, since it seems like Madara believed that Obito had phased partially through the boulder with a Kamui-like power, yet Obito still sustained serious injuries from the fallen rock, so it did crush him enough that he lost an arm and suffered permanent scarring on half of his face. Being crushed doesn't seem like a "kind of crushed" thing. You either are crushed by a rock or you aren't; semi-phasing through a solid object sounds...odd. Yet Obito is injured but not entirely smushed flat by the rock, so I guess the results speak for themselves.
I don't have many good theories to explain this phenomenon, but it's possible that in some cases (perhaps among the more powerful Uchiha users), the latent potential of an Uchiha can sometimes act as a failsafe in moments when the user is in extreme peril, even if an Uchiha hasn't yet activated the Sharingan, or in Obito's case, the Mangkeyou Sharingan. So possibly, in moments of danger, an Uchiha's latent potential can arouse enough to save the user from lethal harm. In Obito's case, the latent potential rescued Obito from death by allowing him brief access to his latent Mangekyou potential even prior to his actual Mangekyou awakening.
Similarly, there is a phase of a "near-awakening" where a Sharingan is formulating but hasn't fully awakened yet.
When Sasuke re-awakens his Sharingan during the Haku fight, his eyes start to lighten before his Sharingan fully manifests, and his visions slowly and lethargically improves as his Sharingan slowly manifests, rather than awakening in an instantaneous burst like it does with Obito.
Sarada doesn't tap into her Sharingan's powers before they activate, but her eyes do lighten and the Sharingan starts to formulate in moments when she is feeling deep sadness and distress (the change is slight, but it is there if you look closely). This happens when she is looking at her picture of her dad and her yearning to meet her father and her grief at his absence.
This lightening happens again during her moment of distress when she reads about the Sharingan and the extinction of her clan in the library, experiencing another strong surge of emotion that causes her eyes to lighten in color, but it's not enough to actually activate her Sharingan.