There are two reasons i'd opt for solo, but I am basing my reply on fieldsports, kayaking and nature watching.
1. There is no doubt that you really get into the zone if you are alone. For one, there is no-one to talk to (out loud) so you will be quieter.You will drift into trance like day dream and through this you will really tune in to all thats going on around you, get it right and you seem to emit less threat and nature starts to accept your presence,its a fanastic tonic for the hustle and bustle of normal daily life.
2. I have wandered fields, woodlands and rivers day and night, and not always in areas I should have been. If you are solo you are far less likely to upset landowners. As a boy I was never sure of the borders where I could or couldn't go, sometimes landowners would ignore me, after I couldn't do too much harm. Others would confront me but after a pleasant conversation about the weather, the crops etc I would gradually become accepted - not so easy if your in a group.
I guess its the same for wild camping. However I do get a great kick when you can show others something they have never seen/experienced, and see their face light up at the wonder of Nature.