I prefer drawing with a wooden pencil as you can be pretty tough on them, whereas mechanicals need a finer touch. In that respect, for accurate analytical stuff a mechanical is great for calmer approaches, but when I go to life drawing classes or if I find myself on top of some car park sketching I'll always take something I can be a little faster and rigourous with.
That doesn't make sense really. It takes more time to bring a mechanical pencil into such a state where it's fully operational than doing the same with a wooden pencil. Actually with the latter there's no such action required at all: it's always functioning properly. You will need to sharpen it from time to time, but the average time of sharpening a wooden pencil is less than the time invested into all the activation processes of a mechanical pencil.