There my be substantial differences, but that will depend on the fare rules for your particular tickets. If refundable, it will not make any difference.
If your tickets are fairly typical non-refundable penalty fares, e.g., you pay $200 + fare difference to make a change to a domestic ticket:
1. If you need to make a change to your travel dates, e.g. push your trip by a few days, you will pay $200 per ticket. Thus, if you have two one-way tickets, the change costs $400 (+ fare difference). On one ticket, changing both segments osts $200.
2. If there are delays or cancellations resulting in a trip in vain, the ticket in question will be refunded. If on the first ticket, you are stuck with a second ticket (what would have been the return).
Thus, you really need to way the up front savings against your own risk tolerance and the cost of the underlying tickets. Thus, a $190 round-trip vs. two $80 one-ways won't matter. Change fees would "eat" both scenarios.