Understanding the difference between a wedding planner and a venue coordinator is crucial to your planning process and to your wedding. If you understand the difference, you'll save yourself some headaches. (And, hey, it's very easy to assume these two roles perform the same duties because the titles are very similar.)
The venue coordinator is there to take care of the venue. She (or he) will take care of everything having to do with the venue (food, bar, etc.). She will coordinate between the bride and the venue staff only. It is not her job to direct your ceremony. It is not her job to ensure that your wedding timeline is followed. It is also not her job to coordinate with the other vendors. And after the meal is served, many venue coordinators leave. They're allowed to leave; their job is done. Because some brides genuinely and innocently don't know all of this, some venue coordinators sadly end up getting a bad reputation when they don't really deserve it.
The wedding planner is there to take care of the bride. She will make sure the venue is set up to your specifications, but her main priority is to ensure you are enjoying your big day. She will stay by your side all day. She will let you know when it's time to cut the cake or when it's time to throw your bouquet. She will bustle your gown. And before the wedding day, she will coordinate with all of the vendors you've hired to make sure everyone is aware of his/her duties and timelines. You will have likely built up a solid relationship with your wedding planner by the time your wedding day rolls around.
I appreciate venue coordinators SO much! They are extremely helpful and valuable. This is just a little more info for you in deciding on whether or not you need to hire a wedding planner.