Originally Posted by Tenchiro
Your hop utilization will be more efficient, so you may need to recalculate that but it won't be a huge difference.
On the contrary, it can be a very significant difference. Going from a 2 gallon partial boil to a full boil will typically DOUBLE your IBU's, which is not insignificant! The first few batches where I did a very large (~4 gal) or full boil, using ingredient kits and not adjusting the hops, did not come out very good because of the unexpectedly high bitterness - it's definitely not a wise thing to ignore.