What is the purpose of feeding an off-center-fed dipole (OCFD) between the center and one end instead of at the midpoint?
Why A center-fed dipole shows a low impedance (around 70 ohms) on its fundamental and odd harmonics, but the center becomes a current minimum on even harmonics, where the impedance jumps to thousands of ohms. Moving the feed point off center, typically about one third of the way along the wire, lands on a spot where the impedance works out to roughly 200-300 ohms on several harmonically related bands. That lets one wire plus a 4:1 (or similar) balun present a usable match on multiple bands such as 80, 40, 20 and 10 meters.
Watch out The choice about resonating over a wider frequency range is wrong because the OCFD is still a set of narrow resonances at harmonically related bands, not a broadband antenna. The common-mode choice is backwards: the asymmetric feed tends to increase common-mode current on the feed line, which is why a good choke is recommended.
OCFD = off-center for multiband match: feed near the 1/3 point, get ~200-300 ohms on several bands, use a 4:1 balun.