Originally posted by reh321 P-TTL has never worked that well for me. Sometimes I use an "automatic" flash {flash measures light instead of having camera do it} dating back to 1987-1995, when I used my Super Program to photograph my infant daughters, and sometimes I use my Canon flash in purely manual mode. Honestly, though, I don't use flash very often .... in most cases natural light works better for me.
P-TTL is great for when you're shooting "situations", rather than taking time to get the lighting just right. You still have to put some thought into it, and make flash / EV adjustments if you've time to do so, but it can produce fairly reliable results in situations where a manual flash would simply be impractical. But I far, far prefer using my cheap, all-manual flash units when the situation allows
Of course, most P-TTL flashes (except for the very base models) allow full manual control too, so if funds allow it's worth having one or more of these...