Following robot, help with the PWM

Hi!
I'm new in this forum, but I have read it long time ago.
I'm doing a line following robot, and I have some doubts. The sensor part is finished.
The motors are going to be controlled with a L293D or L298, the difference between them it's only the maximum current I think.
And my question is: Is it neccesary a PWM control? Can I do it with the micro? How?
Thanks!

There is no need to pwm if you only have 2 line detectors, if you have more then 2, it would be needed or else the extra sensors would be useless.

Ok, I think I have understand it.
I use 5 sensor, so with the PWM I controll the speed of the motor depending on the sensors that detects they are out of the line, don't it?

And...how I can program the PWM? I think I'm going to use a 16f84A or a 8051