AND...Also, when you sell the house, you have to disclose that the addition was un-permitted. If the buyer finds out after the fact that the addition was un-permitted, they can come back and sue you for non-disclosure of that fact, with the damages being how much less the house would be worth if the addition did not exist.
If the city or county find out that the addition is not permitted (one of your neighbors turns you in, or an inspector just happens to be touring your neighborhood when construction is going on), they can halt construction and require you to get the required permits. This may also require demolition of some of the construction already done, to inspect things like foundation footings, electrical, plumbing, etc. They will then charge you at least double the original permit fees as a fine.
It's always best to operate within the confines of the law. Since you know a permit will be required, why consider doing something that you are fully aware could cause you grief down the road.
Considering the future....anything that happens couldn't be good!
Make the right choice.