It shouldn't be needed in any situation.
#1 If it is a result of poor buddy skills, this will be a crutch that will not help develop good buddy skills.
#2 There is the safety aspect of this catching on something and causing problems, not to mention the entanglement hazard.
#3 There is the environmental aspect. How often will the slack in the line catch, drag, snag, or kill hard or soft coral.
#4 If using in low visiblity, just multiple the snag hazard. What if one buddy drops their end of the 10 feet long line in low visibility? Now they are really seperated.