Yes to the first! Emphatic no to the second. If I'm on a roll, I'll keep writing until I run out of words. In order to start writing, I have to make a plan and stick to it, otherwise I'll get distracted and forget. I also have to purge my mind of the idea of "writing mood" because if I wait until I'm in the mood, I end up writing nothing.
Setting aside time to write is a good disciplinary practice. Setting word goals is also helpful, if only so that you can fail to reach them. Failure allows you to better gauge how much you can really write in a set time period. Last month I made myself a spreadsheet to track my daily words, but life interfered and I got very little done. This month I am more optimistic.
Even though concrete goals have a lot of advantages, not everyone can work with them, just as not everyone can work from an outline, and not everyone can write a snappy, plot-driven story. It's hard work to find the routine that works for you, but it's incredibly rewarding once you start reaping the results.