A trenching attachment will cut ground faster than an excavator trench bucket/hoe, as it cuts in a continuous movement. Trencher will cut deeper and narrower. Depth control is easier to maintain.
A trencher digs 3 to 4 times faster than an excavator/backhoe with less mess. To cut a trench, the boom is held at a fixed angle while the machine creeps slowly.
The spoil is excavated more finely with a trencher so the trench can be easily backfilled with better compaction. As the spoil is much finer it is suitable for the bedding of pipes and cables etc.