Visually competiting screenr elements are used when the user needs to compare and make a decision based on the data related to each parameter. For example, when phones are compared they are placed side by side and compared against the same parameters such as RAM, Screen size, processor etc. This approach works also well in Travel sites where flight tickets, tour packages/hotel accommodations are compared. So for each parameter, the user needs to read the corresponding value for each phone. This will force the user to slow down, explore and reflect before taking a decision.
So whenever you have to prevent user from taking a runaway decision, you can force the user to slow down, reflect and take a decision based on the information recieved.
No. If used in the correct context, this will only improve the experience of the user as it allows detailed exploration of the pros & cons. But that will imply 1. More content to be displayed on the screen at a given point in time. 2. May affect the loading time. 3. It may be tricky to show the same screen on multiple screen sizes. Also what users can achieve by simply glancing at the information, the designer should not force the user to slow down. This will create negative effect on the user.
Again, the efficiency of this approach in any context can be determined by usability testing to see if it helps the user take the decision in a reasonable period of time.