Layoffs: engineering/product or sales/marketing?

I see several companies in the middle of layoffs claiming they are keeping engineering and product roles while laying off sales and marketing. 

Is that the best decision? 

obviously we are biased here, but what do you honestly think? 

sure, marketing orgs (as we know) are probably bloated for the most part, but why not just continue to performance manage sales? The odd factor I keep thinking about is we already have quotas at our back with a system that manages out the weak performers. 

Further, when times are tough, it seems counterproductive to reduce your revenue by reducing your sales teams. 

Why not take a hit to R+D with bloated engineering orgs that often lack solid performance management tools? We all know of a few lazy engineers sitting on fat equity packages.

THOUGHTS?