It's weighted as 4 marks for AO1 and 4 for AO3. It's likely that you'll only be able to write 4 marks worth of description for it anyway as it's usually a subtopic that they ask for (e.g. "Outline and evaluate Bowlby's monotropic theory of attachment") or they might specify in the question what they want you to focus on (e.g. "Discuss variations of Milgram's study and its findings"). For the evalutation, one or two (max) good points is enough. It might even, again, specify what to include in your evaluation (e.g. "Discuss Asch's variations and outline 2 limitations").
If it doesn't guide you in the question, I'd go for a decent sized paragraph for AO1 (throw in lots of key words to boost your mark) and either a very detailed evaluation point or two regular sized points.