Trimet - and by extension, many of the LRT systems - need this kind of equipment as they are running primarily single or paired units, with few points of contact with the overhead wire. Even with a headway of only a couple of minutes, this can allow ice to form on the overhead.
It's simpler for many of the heavy-rail systems, as they either have the ability for a single unit to draw from two points (most locomotives have multiple pantographs), or have multiple units all with their own individual points of contact. The first pantograph acts to break up the ice build-up from the overhead, allowing the following ones to have a nice clean wire to draw from.
Dan
Toronto, Ont.