A PPT is the simplest of presentations and contents here are direct. You can have it prepared in a shorter length of time. Flash-based presentations are a bit composite and multi-faceted and are prepared with a mixture of so many media-tools.
A PPT is a flexible format where you can change the content as and when you want without any fuss. A Flash-based presentation doesn't give you that liberty to change the contents so frequently.
A PPT may have to be defined or supported by someone in person who knows the details of the subject whereas a Flash-based presentation is a complete solution in itself. Various media-tools make it a complete resource. You don't need anyone to accompany it to the target-audience.
PPT is a strong tool when you want to initiate someone into your business giving him a concise outline of your effort. Flash-based presentation is perfect for your subsequent interactions as this gives out the details of your business in an elongated and creative manner.
A PPT can be prepared at the minimum of costs with your fund-limitations. But, since Flash-based presentations have varied ingredients and they bear different aspects of your business in details, they are generally costlier than PPTs.
All-in-all, PPTs and Flash-based presentations, both carry a huge significance for different purposes. A Flash-based presentation is erected on facts of your business bolstered by creativity, but a PPT is merely a presentation of these facts in a straight approach, without any major multimedia-support.