When to remove the headrest insert from infant car seat?

[Anonymous]

We have a Graco Snugride 35. LO seems a bit squished, and very warm, with the newborn insert. His head control is pretty good, but I still worry that on a longer drive he may need the headrest. But maybe not. Are there guidelines for when to remove the headrest?

Also, is it intended for safety or comfort?

I noticed that the Chicco KeyFit instructions say not to use it after 11 pounds, but I couldn't find anything similar for the Snugride.