The http://www.coreboot.org/Benefits page says under "possible advantages":
with no detail. (note that the three dots are literally on the webpage, not my paraphrasing).
Support for TPMs /could/ mean support for self-encrypted (Opal) hard drives, but there are other kinds of TPMs (e.g. fingerprint reading) so it's unclear what actually works on coreboot.
Someone in #coreboot hinted (without confidence) that only software encryption is possible under coreboot. Is that true?