Or can it be anywhere as long as the guideline passes through the profile?
I disagree somewhat. I've made plenty of sweeps where the profile and sweep do not physically intersect. They do have to have a similar starting point such as a plane. I'm not sure what is being described as "perpendicular", but you certainly don't have to have the profile and sweep perpendicular at the start. The only time I know that it is critical to have your profile and path coincident is when you have a 3D sketch as your path.
Profile and path do not have to intersect
path does need to intersect plane profile is drawn on
Short answer: yes!
With a sweep it is even more strict: the guideline will have to start perpendicular to the profile as well! If you don't want your shape the start out perpendicularto your profile (or if you are a lazy fart, much like me), try this:
(draw a second profile that is at the end of your shape and) choose Loft, click on the 'Centerline' option and select your guideline as a centerline.
This is how the cables form the sparkplugs on my Rolls ROyce look-a-like engine where made.
A sweep though, is not completely useless. It will make a nice moveable spring for you when used in an assembly! Butthat was not part of your question...
to create a perpendicular plane
Select point at path end