When doing InfoPath 2003 form creation one of the most tedious things that I did was keeping all the sections, tables, fields, data connections and dropdown lists consistent between all forms. When the time came along to pass InfoPath form to the client developers or business analysts it was nearly impossible for them to keep everything consistent because it was so tedious and time consuming. The ROI was not that high for the customer and the client development was pretty slow.
The InfoPath 2007 was released and it has a new feature called Template Parts. Template Parts is a new type of InfoPath template that allows for predefined forms to be saved and then imported into the InfoPath Controls Task Pane. A Template Part is capable of saving Data Connections, Rules, Conditional Formatting, Data Validation and many other things. Just having this capability has saved me a tremendous amount of time when designing forms and it has increased the ROI for the client. A standard address block is one of the first things that I create for a new client because I'm able reuse it right away and show immediate ROI. At first you might not think this would have a big impact but when you take in account that, you no longer have to worry about defining the data source fields, layout table, field widths, colors, font style/size, data connections for states/regions and country, data validation, rules or conditional formatting then the ROI is reached pretty quickly. Once I understood this capability it changed how I started developing forms.
A feature of a Template Part that you need to take in consideration when using them to help designing forms is the Update capability. The Update capability allows for existing Template Part control on a form to be updated once the master Template Part control has changed and re-imported into the designer. At first this capability was frustrating because I didn't design everything with this in mind but after understanding how it worked, I quickly changed how I was designing forms and took advantage of the Update capability.
Long story short, Template Parts are great if you put thought into how you are building and using them. If you don't do this then it will just adds more complexity when building your InfoPath form and shouldn't be used.
Cheers,
Michael