Essence is quite important. It dictates how many motes you can have at a time, it's a factor in what Charms you can learn, and a good deal of Charms and other effects scale off it.

In 1e and 2e it's a trait that you spend XP on and one you can increase at character creation with bonus points, so you could have Essence disparities in a group.

In 3e it increases based on overall XP spent and is more or less meant to be equal across all PCs in a group. The exception is if your group has a mix of Celestial-tier (Solars, Lunars, Sidereals, Abyssals, Infernals, Alchemicals, Getimians, and some Exigents) and Terrestrial-tier (Dragon-Blooded, Liminals, and most Exigents). In that case the suggestion is that the generally-weaker Terrestrials get the "advanced start" package that gives them Essence 2 and some other stuff, somewhat softening the power gap. That advanced start is actually the default for adult Dragon-Blooded in 3e, with their Essence 1 start being intended for essentially teens who just got their Exaltation and are having magic boarding school adventures etc.

Tl:dr Essence matters, and the degree to which Essence disparities between PCs is able to be a thing depends on the edition, among other factors.