The potting soil that I have used for years is the compost I make and I have seen no problems doing that. Some people seem to have drainage problems when they use their compost that I have not had.
I have not attempted to plant in the garden in 100 percent compost, mostly because I have never had enough compost to do that.

The only way that I can see growing with only compost would be in some kind of container but I also think there aren't many things better for a traditional "in the ground" garden than the addition of compost whether mixed in with the soil or just spread on top.

If you are talking about planting just in a container/pot than I think mixing soil and compost together would be worse than compost alone, although I believe there are better options other than pure compost for a potting soil..
Experiment and see what works best for you and good luck.

It is good to incorporate regular compost into your garden soil as organic matter, but it still needs to decompose further before the plant roots can take up the nutrients they need. Mixing in some worm compost will speed up that decomposition and will, by itself, release nutrients that are needed. Those microbes work wonders!

I compost most materials in 25 gallon nursery pots (a hardware-cloth square at top eliminates varmints, though earthworms can enter through the drain holes at bottom). I don't turn it at all. Near the end of filling I put a 3-5 inches of finished compost from elsewhere at top and plant with a tomato or pepper if spring or collards or such if fall and then the warm-season plants next spring. I fertilize but lightly. After one warm growing season everything is rotted and unrecognizable (relatively homogeneous) except the bones. Then I use the compost elsewhere. I may go to 45 or 65 gallon pots.

Great idea gonebananas!

I'm going to have to try something similar this year just to see how well the peppers will grow.

I am doing something similar this year... hope it works out.
i had lots of finished compost so I made 3 raised beds out of 1x6's. they are 2' wide and 8' long. I put down several layers of newspaper of the grass/weeds and filled them with the finished compost and let them sit for a few weeks to settle. when I planted the tomatoes in them I dug out a hole twice as big as needed and mixed in top soil and mulch and then put the plant in.
Even though the compost is done, I'm expecting it to settle, but with all my grass clippings and leaves... I have a never ending supply of compost.

I am trying growing in 100% compost for the first time this year and the results are great. I like the containers because the soil here in Florida near the coast is just like beach sand with little, if any, organic material. Nematodes are also a huge problem in this Florida soil.
I grow in 12-15 gallon plastic buckets that I got from a swimming pool service company. They originally contained 100 pounds of chlorine tablets so a careful washing and drying was the first step.
I put a few holes in the bottom of each pail and filled them with finished compost and set them on top of the lid to prevent ground contact. My tomato plants are well over 6 feet tall, loaded with fruit and for the first year ever, appear to be disease free! We can't even seem to keep up with picking the beans that grow up string trellises just above the buckets, with similar results for all the other vegetables as well.
The only problem I have encountered is blossom end rot on the squash (presumably from lack of calcium) so some amendments will be necessary for certain plants.
I do provide a light fertilizer application with Miracle Grow Blossom Buster once a week but that's the only addition I have added so far.

I've heard the main issue with 100% compost is drainage and water retention.

If you can solve that problem, then I'd say you'll have good results. Since "compost" comes in all shapes n sizes, it's really hard to say what will work.

As to the "must be mixed with soil" statement, I'd say there are a lot of square foot folks that would disagree with that (they use no soil...only compost, vermiculite & peat moss).

Lastly, I don't think many folks have the luxury of having enough compost to use it as their only growing medium. Therefore, you might find it difficult to get some advice from experienced folks (i've never done it, FWIW).

For a few years, I had unlimited access to huge, composted horse manure piles as well as a tractor/trailer combo to haul it, and covered my garden with about a foot of the stuff. and planted away.

Those were the most productive gardens I've ever had - but by the end of the season, most of the composted manure had disintegrated and hauled into the soil by a fleet of night crawlers.

You shoulda gone into the worm business! That stuff must have been teeming with monstrous ones.

I am trying the compost, in self watering containers, but mixing in peat moss with it, seems to be working well so far.

Potted plants generally prefer a coarser mix than in ground plants, which is why potting mixes do not have soil in them (too fine and compactable). The coarser your mix is the better. Compost can be pretty fine especially if you sift it. Not suggesting that you don't use it, just FYI.

I am up in my 70s and no longer go to the composting trouble. I have access to lafge quanities of composted turkey manure. What i do these past several years is wht you might call blending not composting. I mix layers of potting soil and compost. Then mix them together with a earth auger. Mkes some good stuff.