Generally, with this type of work (where I'm trying to go fast), I have to be flexible, so I will often just let nested tasks "die off" after I've found alternative ways of solving the problem or I've changed the idea a bit.

Sometimes I'll delete the nested entries outright, but usually I'll just keep them around until I get to a point where I'm close to completing the feature and then I'll re-visit them to see if they still apply or if I need to reincorporate them into the new design.