I find there is a difference between the spinbike and using your own bike on a trainer. The spinbike is very forgiving, so you might be tempted to neglect your form. On your own bike on the trainer, now that's a different story. I found that out, when I tried "standing" and "climbing" for the very first time.

Also, when you turn up the tension, it is easier to fine-tune it on your own bike than on the spinbike. We have about 10 spinbikes in our training facility and each single one feels differently. On one your have to turn the knob very much, on the next one hardly.

I prefer to use my own bike - never mind the saddle, which is much more comfortable.