At times, some visualizations are used to quickly track specific data points values in a dense area (i.e. line charts with data at the day/hour/minute level). In those cases, the tool tips can come in handy in helping the users to identify the exact value of the data point they are currently looking at.
In most cases, the tool tips shouldn't show immediately as that will quickly annoy the users as they move their cursors over the visuals. However, for those specific use cases where the tool tip should show up quickly, you do have a way of configuring a shorter tool tip load delay.
An example and details are available under: http://microsite.dundas.com/redirect.html?dashboard=66be5ddd-2468-4be9-a548-0c18a529cf49