Bicycles are coming in for tune-ups from having been on a trainer all winter. We often see, and more imporantly feel, a flat spot that develops on the rear tire and talk to customers about road safety. A tire worn by an off season on a trainer can stay on that trainer until it completely wears out. There is little chance you are going to roll over glass during your spinnerval. However, don't take that tire on the road especially this time of year.
Wet conditions and sandy spots are always something to watch out for but when they meet a considerably worn tire with flat spot it makes matters worse. As you corner the tire grips first in the middle then to the sidewall and back again. Having a flat spot can make that transition from middle to center slip much easier.
Factor in that the tire is that much less durable and you'll be begging for road-side assistance. While many of us carry extra inner tubes incase of a flat fewer carry extra tires. Save that older tire for the trainer intensive times and hit the road with new rubber.
A final note on tires is tire pressure. The temperature fluctuations we are enjoying this time of year effect tire pressure by as much as 2% per day. That may not sound like a lot but you will feel the difference on your ride. Checking tire pressure is cheap insurance for your time and monetary investment.