Perhaps the problem is exacerbated by the way that the procedure is used (or certainly has been in the past) at some airports like Heathrow.
In the UK the rules say
Conditional clearances shall not be used for movements affecting the active runway except when the aircraft or vehicles concerned can be seen by both controller and pilot or driver. Conditional clearances are to relate to one movement only and, in the case of landing traffic, this must be the first aircraft on approach. However, when a number of aircraft are at a holding point adjacent to a runway then a conditional clearance may be given to an aircraft in respect of another that is ahead in the departure sequence. In both cases no ambiguity must exist as to the identity of the aircraft concerned.
The bit about one movement only can be interpreted widely - some might say abused. The practice of setting up a string of conditional line up clearances -say, a B747 after the A310, a B737 after the A310, a MD80 after the B737, an A319 after the MD80 and an A330 after the A319 satisfies the rule that the condition relates to one movement only - but is it wise? Then consider that often it is not a variety of aircraft types around the holding point but rather a bunch of similar types all with the same livery. This can easily lead to misunderstandings - and has done in the past. There were some rather amusing
posters floating around a while back on this subject.
OK, not all of the incidents occurred at Heathrow, but using the procedure - which has inherrent potential hazards - in that way focusses attention on it. And if the procedure is withdrawn it may be a case that everyone loses out because of the actions of a few.