Well, strictly speaking on FCP 7 and earlier (since this particular forum is for older FCP...not FCX)...yes, you do. You need to choose the Easy Setup that matches the footage you are using. If you have multiple formats, try to convert the footage to a single format. Don't belive this Apple marketting about "open format sequences."
There are some exceptions...like you can have ProRes footage, and a ProRes sequence...and also edit in HDV or XDCAM footage in that. IN fact, it's best to edit HDV and XDCAM as ProRes. Don't have an XDCAM sequence setting and edit ProRes into that...XDCAM is inferior to ProRes.
Also...don't edit may formats natively. Meaning H.264, MP4, AVCHD...there are many formats that FCP just doesn't work with properly. FCX will even ask to "optimize" the media...meaning convert to ProRes. FCP 7 is a different beast than Adobe Premiere Pro. PPro will allow you to edit formats natively...it's designed to do that. FCP 7 is not....and that's a pretty important difference to know. FCP 7 wants media to be in FCP editing codecs before you start...such as ProRes.