At the end of Stage 15, over 90 riders were outside the time limit allowed for the stage. Included in this group were most of Team Sky. They should have been disqualified from further participation in the race. However, the organisers decided to overturn this rule. Now Froome will rely on these riders to defeat Quintana. Although, Froome himself did not agree with the ruling (here) he may still benefit massively from the ruling.
Organisers of cycling's grand tours put in place incentives to make each day's racing attractive to the fans. There is a stage win. Then there are the range of jerseys that signify the best rider in a category up to that point in the race. And there are rewards from the most combative rider and team, intermediate sprint points, and money. Some teams might not have a potential winner of the general classification and they seek to get their sponsor's name promoted by a variety of these means. For example, they may target particular stages for a win. To avoid the tours becoming only a series of consecutive days of racing there is a minimum effort required on every day. Those who decide to save all their energy on a given day by having a leisurely spin are in danger of disqualification. This is why the decision on Stage 15 has caused so much debate.
Tomorrow the red jersey's destination will be decided. Will it go to Froome with the help of riders who should have been disqualified? I hope not.