Slants are one of the first concepts most QBs learn. It's a relatively simple read, read inside to outside. You can progression read your receivers or read defenders, but the thought is the same, you work inside-out. The simplicity of this read make it a favorite, particularly in areas of tight spacing, because it allows you to read basically any defensive coverage while getting the ball out quickly. It does require reps, because there are a lot of ways defenses can trip up the reads, but once you put in some work, it is highly adaptable and valuable (i.e. it's adaptability makes it relatively cheap to achieve high levels of proficiency).
Banjo Coverage for Stack and Bunch Formations
A favorite way of defending these sorts of formations, particularly in man coverage near the goal line, is to "pattern match" or "switch" based on the receiver's release. This prevents the standard "rub routes" that offenses like to run in these scenarios to get receivers wide open by allowing the receivers to move past this "pick point" before defining the coverage. The most common method is "banjo".
In order to run a "banjo" coverage, the coverage defenders need to be able to see the release of both receivers. Typically what this means is that one defender will attempt to maintain inside leverage while the other maintains outside leverage. It is this leverage that the switch release can take advantage of.
The defender responsible for the "first in" is often going to maintain inside leverage to prevent any quick inside release throw. Similarly, the defender responsible for the "first out" will retain outside leverage to be able to jump any outside breaking route. The majority of the time, this works to the defense's benefit. Even when both receivers ultimately going the same direction (both in or both out), the fact that they are the "second in" can delay the release enough for the second defender to close the tight window, particularly since they are aligned so as to "break forward" on any route opposite their leverage.
But switch releases stress this coverage leverage. That is because, off the snap, the coverage has to respect that the offense is running a rub route, and therefore, must start working to maintain their leverage. In doing so, they put themselves in a disadvantageous position when the receiver breaks back away from the leverage.
Switch Release Double Slants
In a Switch Double Slants route concept, to the QB, the route concept is the same as double slants (although it will likely be paired with a 5-step equivalent drop to allow more time for the route to develop, rather the standard 3-step equivalent). The outside WR will release inside and hard stick the first slant. If he's open, the QB will throw, if he's not, the QB will work to the second WR. This second WR initially runs underneath first slant, acting like a natural rub. This outside release stresses the "first out" defender, forcing him to try to maintain his outside leverage, before breaking back inside on the slant. That little bit is often what is needed for the little separation to get open in the end zone.
(H/T to Coach Dan Casey)
Switch Release Yogi/Snag
This doesn't just work to take advantage or the outside leverage defender. You can also run switch concepts that stress drag/crossing routes before breaking back outside to take advantage of inside receivers
Utilizing Internal Receivers
You can also take advantage of this sort of concept in the slot. Here, Michigan goes to a trips formation with a stack with two receivers in the slot. This is going like a smash concept on the outside with an inside slant. The inside slant acts as the first, quick read, and then you progress to the smash concept. But the idea is the same. The defense is going to "banjo" the stacked receivers. Because of this, the 2nd receiver is going to have a slight outside release, and while the first receiver works mostly to get vertical, he stems slightly inside. This dictates the coverage. This is important. Because the slant receiver is going to have a defender with outside leverage on him; he gets to work away from the leverage. The corner route as part of the smash concept is going to have a defender with inside leverage; again, the receiver gets to work away from leverage. Because of the stack formation and the "quasi-switch" release, the coverage has been dictated in the offense's favor, with neither route being capped.
(Note, Michigan here also used motion to better define the coverage as man-to-man, motioning into the stack formation, but then waiting a beat to allow for Maryland to communicate the banjo coverage because Michigan wanted that coverage with this call).
Banjo coverages and other match-up coverages are a great way to mitigate a lot of things that offenses want to do, particularly near the end zone. As defenses get smarter and more complicated on the back end to be able to apply tight coverage against stack/bunch sets, offenses have started responding in various ways. The best offensive minds understand well defensive football, because each defense and coverage has weaknesses. Forcing the defense into known or defined coverage will only better help your offense execute. Switch releases from stack/bunch are one of the best ways to get there.