The task weight is the setting to allow you to basically determine how much weight to give your allocations. For example, if you asked people of their next 10 shopping trips, how many items they would purchase, you could choose to set the task weight as 10. This would treat each allocation as a separate decision as far as the utility modeling is concerned. A weight of 5 would half the weight and not treat each allocation as a separate choice, and a weight of 1 would treat it like a normal discrete choice. You can think of it like repeating the choice task in the data set.
It's hard to know exactly what the weight should be. The software defaults to 5, but it's kind of up to you to decide how much do you think people are just putting allocations together, versus thinking about each one independently.