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Usually TOIL (when I've worked it) has been something like 1.5x so if a specific project needs a couple of days extra work over a week to get it done, I've done it and got 3 days back in return. Even 1x is not bad if you do it every now and then but I know people who are doing it regularly.
The problem is if, as an employer, you're regularly having your teams do overtime for TOIL, you're stuck in a death spiral. The team have to take the time off so they're not working so they need to work more overtime to keep up. My last UK employer only did paid overtime for that specific reason.
Depends if you consider a day off as working for free. I never minded an occasional day of TOIL but every month is bullshit.
See also - traveling for work on your own time. I've had bosses who were surprised if they had me travel on a weekend or bank holiday and I claimed TOIL for those days