I'm about to accept a job with a 90 day probation period. What does this mean and why do these exist? I've heard an input that after that period my salary might increase slightly (my salary is almost 10k below average for engineering). Does this mean if I don't perform to their standards they could decide to let me go after those 90 days or earlier? There's not much in my job offer that states more about it, but days off and vacation begin after it and so do benefits I believe.