Since SharePoint 2010 was released I’ve been a huge fan of Managed Metadata. I think it is a very powerful and still relatively straightforward way of managing your metadata. Ideally I would want to manage all of my metadata in a central location, if only for maintenance reasons.
This is also why several people thought the old Choice field would be used less and less.
Storing *all* of your metadata field values as Managed Metadata is however going to be a problem if you’re in an environment with many content types and especially many columns inside those content types that have a list of values to select from.
In particular the first issue I recently ran into was the fact that my Datasheet View wasn’t opening, because I crossed the maximum of 8 lookup fields. Only 8?? Yes, only 8. A number that any decent set of content types should have no trouble reaching.
Sure you can overrule this setting in Central Admin, but there are plenty of (performance) reasons why you shouldn’t do that.
So how do you get around this? Well, unfortunately this means you shouldn’t assume that will store all your metadata fields as Managed Metadata. It means you should look at each of your columns that allow for selecting a value, to see what the best location is to store those values. And if you’re concerned about performance, your best bet is the Choice field!
How to decide then when to use a Choice field? As a rule I would say: Managed Metadata is there for metadata that actually needs managing, in other words, metadata where you expect values to be changed from time to time. So if you have a column describing the possible values for the direction of an elevator with the choices being “Up” or “Down” (assuming you are not in Willy Wonka’s Chocolate Factory), then there isn’t really a point in making this into Managed Metadata. In such a case, stick to the good old Choice Field. It’s less manageable, but for a field that’s not going to change that doesn’t really matter, and it will help you stay below the Lookup field threshold.
For a more elaborate comparison between Choice field and Lookup field, there is a nice PDF here.
Marc Anderson also wrote a good post summarizing the impact of crossing the lookup threshold, and why you should still look at alternatives for each field.