I bought a trainer from Performance several years ago. The advantage of trainers are:
The bike fits me, crankarm, tt length is correct, etc. so I'm comfortable.
I don't schedule my workouts around the weather. Today we have freezing rain. I will ride an hour on my trainer. I'm warm, safe don't have to worry about icy roads and freezing hands and feet and I get my workout in.
I can ride when I want, don't have to rush out of work to beat the darkness. If I know I'm going to have a busy day and get home late I can get up before work and ride.
It's easier to work on technique and do interval training on a trainer and I burn about the same amount of calories
I can still ride while injured.
Trainers can be boring without a plan, music and a heartrate monitor.
I follow the plan in "The Female Cyclist" and use music I bought from a company that sells workout music www.powermusic.com
. They have all kinds of music with a variety of bpm. Makes it easy to get your heartrate into your training zone.
I have an mp3 player and its easy to change the music so I don't get bored with it. Its also very small so it fits in my jersey pocket.
I also use the workouts from the book "The heart rate monitor workbook" by Sally Edwards.
When I ride I dress as if I were going outside. I wear cycling jersey and shorts, my shoes, socks and gloves.
I also use two fans, a ceiling fan and a fan on the floor. In the winter I usually don't overheat.
I keep my rides to an hour, sometimes a little longer. That way, I don't get so bored.
My bike is always set up on the trainer, that way I don't spend time preparing it to ride.
Hope this helps you decide.