IMHO I think it's a 'must' have.
Power outages. Which you WILL encounter more than once in your lifetime RV'ing either the CG's power grid problems and/or from storms taking out their electric.
Being able to run the ac in the coach while you are driving. Pretty much a given if you have pets on board and driving in hot weather.
Same for stopping at a rest area you will be able to use everything inside the RV with a gen.
Since you are ordering your MH I would definitely order the generator at the same time so it will be under the new coaches warranty.
Good luck on your new adventure! :C