Both Cebil and Yopo seeds include a lot of fats and alkaloids, in addition to 5-HO-DMT, 5-Meo-DMT and N,N-DMT. Toasting the seeds causes a lot of those alkaloids to vaporize off, leaving you with just 5-HO-DMT (which has a very high vaporizing point).
The only real problem with it is that if your seeds contain N,N-DMT or 5-Meo-DMT, those two will be destroyed in the process.
If you're doing an extraction, it's really a matter of personal preference, although I generally toast mine.
Blessings
~ND