Emily Oster covers this in her book Crib Sheet. For very young children, there's an increased risk of smothering, although it's still very small. The primary effect, IIRC, is that parents get worse sleep. Long-term outcomes for kids are insignificant.
Here in India, it's kinda normal. The houses are way to small for poor and middle class people. Children upto an age of say 10 to 12 cosleep with parents. The normal is changing in cities and towns, though!
At personal levels, I don't know because I'm close to experiencing the parenthood. But, I've a plan not to affect sex-life after our first child. We live in a combined family in India. The child will sleep with the granny or gran'pa!
Based on the experience of all previous generations, we can say with confidence that everything depends on age. Before entering school, children are almost everywhere and always sleep with their parents in bed or in the room where the parents sleep there is a children's bed. And after a child enters school, he is usually allocated a separate children's room. Does it have an effect? More likely no than yes.