The potting soil in question is in medium to large sized pots that had/have tomatoes or small fruit trees in them.
The only two problems I can think of would be disease and nutrients. There are some diseases (eg. fungi and nematodes) which will linger in soil, so you really need to treat the soil or discard it to somewhere where the disease is not a problem (ie. a different kind of plant).
As for nutrients, these could be topped up with liquid feed or top dressing. I find potting compost settles / compacts quite a bit so there's usually space for top dressing each year. I also re-use potting compost by putting it on raised beds or filling small hollows in the lawn. It isn't the best medium for the latter, but every little bit helps.
It all depends on what was initially potted inside of the soil, to add onto @winwaed you can actually boil some water and pour it into the soil to kill any bacteria or disease. The other thing you can do is use some fungicide to get rid of anything harmful.
Although top soil is fairly inexpensive its a major profit margin for these garden retailers like home depot, lowes, randazzo's, etc. They want people to toss the stuff out and buy new soil each and every year. To me this is a total waste of money and another way to make a dollar off of you. To you a bag of decent top soil is a mere 3-4 bucks...but multiply that by thousands of people buying that stuff and this could be just for one store!
You can always mix it up with some new soil if you still insist on buying new top soil.
Crop rotation My grandparents had а large garden beside the vineyard, that they cared about long years. Every spring, they reshaped the garden - putting the tomatoes, cucumbers, pumpkins, carrots, onion, cabbage and other goodies in new places. They told me this is because every plant uses some same assortiment of nutrients in the soil. Planting the same kind of plant in the same spot for several concessive years would exhaust the soil, they explained. Later, at the university, the teacher in Engineering Ecology told us planting the same crops in the same place is one of the biggest problems of contemporary agriculture.
Adding compost I have read that compost not only supplies the soil with nutrients, but also aids texture. This summer is my second year of balcony gardening. I use the same soil as wast year, mixed 3:1 with compost. I compost most of what I harvest and don't use (stems, leaves). Everything is growing fast & healthy for now, so let's hope this works out forever :D I would really love to be closer to sustainable.
Plants in pots need every ounce of care we are able to provide. Potting soil is pre-mixed and sterilized. Disease is a deal breaker. Clean, fresh soil and a little bit bigger pot once a year is the best insurance I can imagine versus losing my plants(s) slowly but surely to death. In-door plants are long-term perishables. Some longer than others...we can give our plants an 'edge'...it isn't a big deal to make your own soil. I've done it. I've decided that it was much more cost effective to use a ready-made product. Sterilize your own and let me know how that works out!
Potting soil now comes infused with important bacteria and mycorrhizae to incorporate life back into the sterilized soil. Lots of decomposed (and non-decomposed) organic matter fluff up the mineral content.
During the seasons, the organisms in the soil eat up the organic matter that once fluffed up the potting soil. Top dressing with decomposed organic mulch every month or so would prevent the compaction that occurs as organic mulch is used up within the soil. Otherwise your plants are trying to survive in depleted, brick-textured soil. To top dress too late or to use non-decomposed organic matter might take longer than the plant can live to be useful to the plant.
I put my indoor plants outside during the summer on a protected porch. Seems to rejuvenate my plants tremendously. I also include new potting soil, no rocks 'for drainage', never add garden soil, put tiles beneath the pots to increase drainage. I enjoy getting a new pot or two every year and my plants always look greenhouse-new. Also, I use extended release fertilizer, sparingly and when I water everybody goes into the shower, gets drenched in cold water, drip dries then back out into their normal spot. They don't get water until each is as dry as the plant can get without undo stress. Any sign of insects or disease I've got my handy-dandy loop and microscope to KNOW who my plants guest are...great tools!!
Potted plants are prisoners OF their pot-world. Using depleted or disease tainted soil is just a big NO-NO and a needless risk that doesn't pay for itself. Hope this helps!