Using analogWrite on transistor(s)

As i'm clearly not electronician man, i was wondering if the duty cycle of the PWM signal wasn't bad for the transistor's life ?

I'm not very familiar with all these things that's all.

I already tried using a TIP120 on my arduino on an analog pin. It works fine.
But, all i was wondering was only if PWM signals could damage the transistor on long term ?