This is a waiver used in certain cases where a visitor would be ineligible to visit the USA for many reasons covered under Section 221g, the purpose of the waiver is for things like humanitarian reasons such as medical grounds like not being able to get medical treatment in their country.
Intelligibilities covered by 221g can be found here:
http://travel.state.gov/visa/frvi/ineligib...ities_1364.htmlQUOTE
GROUNDS COVERED BY THE WAIVER
A waiver under section 212(d)(3) of the I.N.A. allows nonimmigrant applicants to overcome many grounds of inadmissibility. Some of the grounds that are covered by the waiver include permanent grounds of inadmissibility, such as fraud or criminal conduct, as well as some grounds that are limited in duration, such as previous unlawful presence.
http://www.h1base.com/page.asp?id=311This is not used for spouse or fiance to visit USA while petition is being processed.