I was reading about [pseudorandom number generators](https://en.wikipedia.org/wiki/Pseudorandom_number_generator) and how they need a seed and how that seed is usually current system time in milliseconds. One of the most common algorithms is the [linear congruential generator](https://en.wikipedia.org/wiki/Linear_congruential_generator), which is an algorithm that based on some fixed constants and this seed through some mathematical computations gives the final pseudorandom output. 

But what are the disadvantages of using this time directly as a pseudorandom number?