Here is an example of why leaving the resampling option of Lanczos8 checked is recommended, even though it will take a good amount of time longer:
A 100 x 100 image made using no resampling.
The same image made using Lanczos8 resampling.
As you can see, using resampling gives much better image quality, so unless you are in a real rush it is recommended to use it.