It simply depends on what you want to accomplish. The QB programs are tools. You can use one hammer for everything, or the Right Hammer for the specific task. Tools are just tools.

For instance, if you really manage your projects closely and do project monitoring, estimates vs actuals, cost to complete, need to watch for Overbilling from Engineers or subs, etc, then again, QB Online doesn't have these tools. QB Premier Contractor, for instance, allows you to use an Estimate for your initial Scope, PO for partial draw requests until the project is complete for Subs' labor and for materials, and even run Cost to Complete compare to Estimate Vs Actuals, to manage close margins and profit. I will give you one report as an example, that isn't in QB Online.