It partly depends on where you train. Some course providers have less paperwork, or at least less comprehensive paperwork, for their students to complete than others. This can make a huge difference to the workload. The workload can even change from year to year on the same course; I have to do more in some regards than last year's students because the university chose to change the way weekly reviews are conducted and now expect a greater amount of evidence for each standard than they previously did. Then there's the ever increasing list of directed tasks that changes from year to year... If the course provider is not particularly prescriptive about what and how things need to be done; the workload is easier to manage. The expectations of placement schools also play a big role; some schools don't require in depth planning to be made available whilst others do, particularly if these plans are shared.
I don't really know what to make of people who claim that they do not plan differently for observed lessons. I am quite happy for my children to create some slightly impolite expanded noun phrases when I am not being observed, but I am not going to give them opportunities to do that during an observed lesson because the observer might not have the same sense of humour that I do. Either on a conscious or subconscious level, the fact that you are going to be observed by someone with potentially differing sensibilities will surely inform planning. Additionally, the expectation of an observed lesson is generally that you will give the observer the opportunity to assess your teaching adequately. If you had planned to administer a test or have the children write the final draft of their independent writing, but you've discovered that someone is coming to observe that lesson, I find it hard to believe anyone would choose not replace the lesson with something else. A lesson that is almost wholly a summative assessment of the children will significantly narrow to what extent the observer can assess the teacher against the standards and that is unlikely to go down well with them.