Sometimes the dose does not fit the barrel. The volume exceeds the syringe, or the number lands at the very top where the plunger sits awkwardly. The instinct is to draw twice, and it is worth being clear about when that is fine and when it is a bad idea.
Splitting a draw doubles the number of measurements, and each measurement carries its own reading error. Two readings of roughly half a dose are less accurate than one reading of the whole dose, not more. So splitting always costs accuracy.
It also doubles the number of vial entries, which matters for a preserved solution that is going to sit for weeks.
When is it acceptable anyway? When the alternative is worse. A dose that genuinely exceeds the syringe capacity has to be split or not given, and split is better. A one off situation where the right syringe is not available is a reasonable use of judgement.
What it should never be is a routine. If every dose requires two draws, the concentration is wrong for the syringe, and the fix is at the next reconstitution rather than at every injection for the next month. Choosing a stronger mix so the dose fits in one draw is a five minute decision that removes the problem entirely.
If you do split, record it. One row, the total units, and a note that it was two draws. The note matters because a split draw is a plausible explanation for an odd week, and without the note you will never consider it.
Sorting the concentration out for the next vial takes a moment in a reconstitution calculator. Comparing two or three candidate volumes is faster than living with an awkward one.