I started camping 40+ years ago--and have been a hiker for roughly 35 years. I'm an Eagle Scout, spent 13 years as an Army officer etc. So, I have been outdoors a great deal. In recent years, I have been primarily a hammock hanger.
HOWEVER, a hammock--with tarp, (& mosquito netting) and some type of insultation under me--is not always "ultralight". (My Hennessey Ultralight Backpacker is roughly 2 lbs). Therefore, there are times when I leave the hammock home (to reduce pack weight) or because a lack of suitable trees in the proposed hiking area makes hammock hanging not very practical.
My biggest problem with using just a tarp (which I have done many times in 40 years) is dealing with "critters"--especially of the mammal variety. Depending upon how you choose to pitch your tarp--you are basically fairly open on one (or all) sides to "invasion" by curious animals. Approximately 27 years ago, I had a skunk enter my tarp---it left without spraying. Six years ago, I woke up to a stray pitbull licking my face. Then, you have the occasional mouse, squirrel, chipmunk that explores your tarp area. This sort of thing doesn't happen frequently--but it happens enough to get one's attention.
Generally, I just "deal with it"--it goes with camping "on the ground". However, I am always open to learning other people's ideas regarding how to reduce the problem. (And, I am open to hearing other people's stories regarding their close encounters with critters and tarps).
NOTE: I don't keep food with me where I sleep. Except in really bad weather, I don't prepare or eat food where I sleep. I take steps to reduce the amount of sweat/salt stained items that are on me--or in my sleeping area