common claim that constraints feed creativity. But it doesn't have to be so; constraints may, well, constrain creativity too.
I use mnemonics such as SFDPOT in my testing. Seeding thoughts with each of the specific areas encourages idea generation but throwing away ideas that come from it, perhaps because they don't seem to fit into that category, holds it back. Ideas often form chains, and it may take several "invalid" links to get to a "valid" one. Breaking the chain loses that opportunity.