I never really had a problem with time limits before university, but after doing university exams I think some of the time limits are ridiculous. As a maths student, I like to take my time to avoid clumsy errors, and I find with some of the exams you would have to work extremely quickly and without hestitation to give a full answer for everything.
Think of it in terms of being an employer, you might have two candidates who both achieved a 2.1, however candidate A didn't rush and unfortunately didn't have to time to answer everything, whereas candidate B finished a bit quicker and achieved the maximum possible mark he would of earned given an endless amount of time. While those two may have the same mark on paper, I think I know which one I would rather hire (that is of course, if we're hiring soley on academic achievement).