While there are many reasons a channeller would want to bring energy towards or into their body, there are just as many times when the reverse is desired. Flaming dragon breath, bolts of lightning, or other hazards of adventuring life are also forms of energy, and the channeller would like nothing more than to move them far away. The personal force field is a spherical shell that can aid in repelling such attacks. However it takes a lot of energy to maintain the field, and this drain spikes when the field is actually struck. It should be noted that channeller spells can pass from inside the field to outside, but many other spells cannot. Furthermore the field is an energy effect, not a physical construct, so while it will allow air to pass through the same can be said for arrows and swords.