Hayden Smith: The benefits of using share units instead of dollar values are evident when scheduling trades before the market opens or after it closes, or when prices fluctuate between initiating a trade or its execution. Currently, when using dollar values, I need to calculate the current price multiplied by the number of shares or the total value I wish to purchase. I then add a margin of safety (MOS) to the trade for potential price fluctuations during my market order.

However, this approach becomes particularly problematic when dealing with high-priced shares. If the margin of safety is insufficient, there's a possibility of having several hundred dollars remaining uninvested. This occurs because the MOS did not cover the purchase of the final share due to insufficient funds in the order caused by the price fluctuation.

For example, without a MOS, let's say I have $5,000 in my account want to buy approx $3,000 of a VTS priced at $300 each and approx $2,000 of VAS. If I initiate my first trade at $3,000 of VTS I should have 10 shares. However, if the price fluctuates and reaches $300.05 before the order executes, I would only end up with $2,700.45 ($300.05 x 9) invested in VTS which would then leave me $2,299.55 to invest in VAS, which has significant altered the amounts I wanted in VTS and VAS due to a tiny price fluctuation.

If I were able to select the number of shares I wanted to buy, 10, my trade would have executed at $3,000.50 which is much closer to my target of $3,000 in VTS and $2,000 in VAS.

By enabling the purchase of shares in units, I eliminate the need to calculate a margin of safety based on dollar values. Consequently, any price fluctuations would not hinder my trades as long as I have sufficient funds in my account.

Cameron McCay: Hey Cameron, thanks for this! It makes sense why you wouldn't want an order to go through with N-1 share units instead of N.

In the scenarios where we can't fulfil an order for N units with available funds, would you be happy if the order failed?

Hayden Smith: In this scenario I would still prefer to purchase N-1 units. However, if the order would fail instead of purchasing N-1 units, I would still use this feature and try to make sure I have the funds available.