google says:
Low Weight
Because they are more efficient, toroidals can be up to 50% lighter, (depending of power rating), than traditional E-1-transformers. Low weight simplifies end product design by reducing mounting hardware and supporting enclosure requirements.
Small Size
Most toroidals are smaller than their E-1-transformer counterparts. Electrical and mechanical designers, when "painted into a corner" by a minuscule space allotment for power supplies, appreciate a toroidal's compact dimensions.
Flexible Dimensions
compounding the benefits of low weight and small size is the flexibility to vary dimensions. As long as the core cross section is held constant, the height and diameter for the toroidal may be economically varied to accommodate equipment design requirements - a great help when designing low profile, slim line equipment.
Easy to Mount
A single center bolt easily and quickly mounts the torodals, avoiding costly mechanical design and practical problems associated with traditional E-1-laminated transformers..., and three bolts are eliminated at assembly.
Low Stray Magnetic Field
Toroidals have no air gaps: primaries and secondaries are wound uniformly around the entire core. As a result, toroidals emit very low radiated magnetic fields. This makes the toroidal ideal for application in CRT displays, high quality amplifiers, and medical equipment.
Low Mechanical Hum
the core of a toroidal s formed from a single strip of grain-oriented electrical grade silicon steel tightly wound in the form of a clock spring with the ends spot-welded i place. the copper wire is wound over polyester film, forming s silent, stable unit without give or varnish coating.
Reduced No-Load Losses
Compared to traditional E-1-transformers, toroidals exhibit extremely low no-load losses. In applications where a circuit is in a "stand-by" mode for long periods, the potential cost reductions for power can be significant.
