It changed. Maybe depends on area? IDK.
I used to temp 20+ years ago. It was almost like being self employed but without having to do tax or advertising or anything like that, the agency did it all, you worked and they paid you. The wages were good, I'd always be on more than the permanent employees doing the same job, to reflect the lack of holiday pay/sick pay/and the fact they could end my employment at any time for no reason. If I wanted time off I'd just speak to "my boss" at the placement and tell them I couldn't work tomorrow or next week or whenever it was, asking them if they'd cope without me or if they wanted me to tell the agency to send a replacement to cover me. I never used to tell them the reason, I didn't work for them and it was none of their business. Sometimes I was ill and needed a rest day/week, sometimes it was a holiday, sometimes an interview. Some of the long term temp roles would get you to train up a replacement temp for a few weeks then not have you back if they knew you were going for interviews. There was plentiful work and no pressure to take it. I'd be told about a job, often they'd be pleased if I could start that day, they were grateful to have me.
At one point I went permanent for around 5 years and when I returned to temping I didn't last long! I was living in a different area so maybe it was that, but things had changed. The agencies all wanted me to sign a contract, which never happened before. Two of the things it said was I'd not take time off during a placement, unpaid "annual leave" breaks would have to be between placements and I'd have to give the agency notice if I wanted to terminate the placement. Some of the temp jobs required interviews (unpaid), which I felt was taking the piss since they could fire me at any time with some or other excuse. The wages were shite, usually minimum wage or thereabouts with a "holiday pay element" added on to try to fool you into thinking it was better, when the permanent employees would be on more than that and getting one month's paid holidays, job security etc too. They'd moan if I got lost trying to follow their hokey directions and showed up ten minutes late. Placements generally treated me as "lesser than" compared to the permanent staff. There wasn't as much work available and I was expected to take it if offered, the agency seemingly offended if I didn't.
There were no advantages to it for me any more. The whole point had been the flexibility to take time off whenever I felt I needed it without getting quizzed about "how ill was I really", freedom to job hop whenever I felt like it and usually only work 9 months of the year - whilst getting paid the same wage as a permanent staff member working all year barring their 2 week annual leave, that they had no legal entitlement to but was the norm back then. The new way of doing things was rubbish by comparison so I gave it up.