I don't think that there's anything inherent in tiling managers that mean they have to be light, but it's very common for them to be light. Ratpoison, xmonad, awesomewm and i3 are the most well known tiling managers (unless I've missed any out?) and all of them are very minimalist and resource light.

My non-expert take on this is that the sort of person who sees value in the efficiencies from using a tiling WM are also of a kind to use system resources efficiently too, even though they are orthogonal characteristics.