By planning your video content in advance, as is done at the strategy stage, you give yourself the opportunity to more efficiently and effectively create that content. Filming and editing footage in batches across multiple videos allows you to embrace economies of scale. If you're producing a lot of similar content then video templates can help you keep a consistent look and feel to your videos, in line with your brand. Basically, as with most things in life, planning ahead saves you time and money in the long run — and more importantly it sets you up for success.
Professional cameras, like DSLRs, give you fine control over the manual settings of shooting video and allow you to achieve the shallow depth of field (background out of focus) that people rave about. While they're primarily used for photography, DSLRs are incredibly small, work great in low light situations, and pair with a wide range of lenses — making them perfect for video. However, DSLRs do require some training (and additional purchases) of lenses.