For Australia, a CAD was required to finance our mining boom (capacity and capital constraints) due to our savings and investment gap. So yes, in this sense a high CAD was beneficial as it generated employment and business revenue (though some of this leaves Australia as debits in the primary incomes account). However, if an economy accrues large amounts of foreign debt and equity without gaining some significant benefit in return the outcome could prove to be adverse. This may result in a widening CAD and ultimately a debt trap due to large amounts of servicing costs obligations. Further impacts include the loss of investor sentiments and its associated transmission effects (i.e. greater FX volatility, more contractionary fiscal policy and all that shaz).
Usually, the CAD is considered as a percentage of GDP. If I recall correctly, anything exceeding 4% is considered detrimental? <-- Don't quote me on that
To answer your question in short: a CAD has mixed impacts.
