Not quite as simple as profitability and efficiency.
For example.
If the colonies food status if favorable, the colony will only exploit highly profitable sources.
But if the colonies food status is poorer, the colony will exploit most food sources regardless of profitability.
The amount of nectar intake matters also.
If a colony has a low nectar intake, a highly profitable source is desirable.
But it the colonies nectar inflow rate is high, then a highly profitable source may not
be required or even desirable, because the colony must maintain a regulated nectar inflow rate.
This is why honey which is set out for the bees during the main flow is rarely touched by foragers. The honey is perhaps the most profitable source available, but is ignored by the bees so the colony can maintain its current nectar inflow rate.
Best Wishes,
Joe
"Here their delicious task the fervent bees,
In swarming millions, tend; around, athwart,
Through the soft air, the busy Nations fly,
Cling to the bud, and, with inserted tube,
Suck its pure essence, its ethereal soul;
And oft, with bolder wing, they soaring dare
The purple heath, or where the wild thyme grows,
And yellow load them with the luscious spoil."
-Thompson, 1730 A.D.
http://pets.groups.yahoo.com/group/HistoricalHoneybeeArticles/