Using the Pro Tools Tempo Ruler gives you a lot of creative ways to visually change your session tempo's. It gives you the ability to use multiple different tools and methods to change the tempo. In many ways, using the tempo ruler is similar to writing in track automation.
Using session templates in Pro Tools is a great way to speed up your workflow when creating a sessions. It lets you get to creating music faster and less time setting up tracks and plugins. When you create a session through a session template, it will contain all the internal settings of the session its created from. This includes tracks layout, tempo, audio, midi, I/O settings, buss and insert settings, plugins, etc. This can have a lot of advantages when using vi's with aux output stems, various templates for songwriting, or even when live tracking with a band.