I'm not saying that it's every day or even every week but occasionally, in the right circumstances, I believe some children should be able to work independently of an adult. Many of my statemented children have IEP targets to rely less on adult support.
Also, I work with a different group each lesson, and when I work with the statemented child's group I may ask the TA to support another group. The child is being supported, guided and assessed by me and I think it's unfair to leave the other 26 children unattended while the 4 I'm working with have me and a TA.
Saying that there are some circumstances where I would never want the TA to leave a child's side.