Channeling a bolt spell imposes a 3 second hard roundtime in exchange for a higher chance of hitting a vital area and subjects the attack to less critical randomization. Specifically, the critical randomization floor is decreased by 1-2 ranks (depending on the actual critical) and the chance to hit every location is the same at 7.7%.
Even more specifically, when a bolt is CAST/EVOKEd, it has a little over 16% chance to hit the eyes, head, or neck. A CHANNELed bolt has over a 30% chance. Most of those locations will also result in a critical kill for ranks as low as 5 or 6. While it will take 7+ against the chest, abdomen, or back. If it is determined to be a rank 9 critical wound, critical randomization can lower that all the way down to a rank 5 (typically non-lethal against vital spots). If the same bolt is CHANNELed for the same rank 9 critical wound, crit randomization will not lower it less than a rank 7 (typically lethal against vital spots).
The roundtime imposed by channeling cannot be mitigated by any haste effect.