Generator 'necessity' will depend on:
1) How frequently you anchor out. (More importantly.....)
2) How many consecutive days do you anchor out at a time?
3) How much power you intend on consuming.
4) Power Storage (battery bank size)
If you anchor out every weekend, but only for one night (Sat. -Sun.) you could easily get away with a decent sized set of batteries on the 'house' side. However, if you intend on running TV's, Stereo, coffee makers and a microwave, you may want to consider a generator.
I have 2 group 31 AGM batteries for the house. I also have a Honda 2K portable generator. I don't have a TV and have no electrical heating elements. I've sat on anchor for 10 days and only run the generator for 3 hours every other day (or 1-2 hrs daily). Sometimes a little more if the admiral wants to keep the fridge turned up to keep meat frozon in the fridge, or if we've been playing the stereo a lot. I can heat my hot water tank in approx. 15-30 minutes. That includes playing the stereo for approx. 6-8 hours per day.
Our stove is butane, our grill is propane. Our head is a manual flush. Out lights are LED. We use a footpump to inflate the dinghy.
It's a balance of power consumption, power conservations (need vs. want), power storage and generation. If we're going to over night (sat. - sun.) we don't even run the generator.
It's up to you whether you need a generator or not.