C Assists aren't very popular in Dragon Ball FighterZ right now but might be in the future according to KnowKami
C Assists in Dragon Ball FighterZ have an off-putting quality to them that make it so that most players don't use them as often as A Assists and B Assists. While C Assists are typically very powerful, they tend to have longer cooldown windows to limit how often they can be used.
Some players, like PGP|TheCoolKid93, are big believers in C Assists in Dragon Ball FighterZ. Although they're not without their downsides, KnowKami recently released a video that has him talking about how C Assists could end up being more relevant in the the meta's future.
One of the best aspects of assists in team fighting games is that they allow a player to create pressure without committing their point character. Essentially, a player can force a favorable rock-paper-scissors situation even from full screen.
However, it's believed that it might be better to simply "take the hit" from the A and B Assists in certain situations sense it'd only result in a loss of health. Following this, you can quickly reengage the opponent in the neutral.
As C Assists are stronger, they could potentially allow for more combo scenarios. Intentionally getting hit by assists would be less ideal if this ended up being the case.
Of course, the tradeoff (as previously mentioned) is that C Assists do take longer to refresh after usage.