That's a very important question. I think you've zeroed in very quickly on why it's there. The main purpose of this leave is to provide people in untenable situations with support quickly. Being charged with an offence is dealt with through a formal legal or justice system exercise, and as you say, it can be timely. It can take much time.
Based on common law jurisprudence, an employer cannot take frivolous or vexatious allegations or hearsay, say, from a false accuser in making their decision about whether the employee is entitled to take the leave or not. In addition, the provision is very clear that the employer must consider the circumstances of the individual claiming the leave and assessing whether it's probable that the employee committed the offence. Probability at law is much more than just possibility, so the threshold is set quite high for denying the leave.
Again, as in the case of the leave for traditional indigenous practices, the risk that someone would take 10 unpaid days off is probably quite minimal.