You need to review just how you are going to use it to determine what your battery needs are.
A winch can run down a battery to the point of stalling the engine and it won't have enough to restart the motor. Ask me how I know that in the middle of a severe blizzard. This can happen from welded solenoids or extended heavy useage.
Loads can be left on the main battery and run down the battery as in leaving an interior light on over night.
Typically for short pulls the single battery will provide adequate voltage/power to handle the winch load.
My main reason for installing 2 battery systems is I have a tendancy to travel alone and have to depend on myself and my equipment. Usually isn't someone there to do a jump.
In order to cover most bases, I installed a second battery and a 2nd alternator in place of the A/C compressor. This accomplished a number of things. It provides a backup battery if the main battery goes dead. I installed a momentary switch and solenoid to parallel the batteries if the main one was dead.
It also provided the capability to parallel the batteries for extreme winch loads. It also provided a backup alternator if one failed. I used an external regulator so I could jumper 12v to the field of the 2nd alternator and get 120VDC out of the 2nd alternator to power brush type tools like drills, etc. That was before battery powered ones were so available. Also, you can use the 2nd battery, or both as a welder.
You could also take one battery out and use it remotely to help another vehicle, provide camp lights, etc.
Today, I would probably use an internally regulated alternator as my 2nd alternator and forego the 120VDC option.
You can use a continuous duty solenoid between the two batteries and have it energized when the ignition is in the run position. That parallels them only when the engine is running and they should charge just fine. That way you wouldn't need the 2nd alternator.