It always sounds like a nice plan, on paper, “unlimited time off”, who wouldn’t want that? You if you are smart.
Problems with flex-time:
You have to know exactly to the second how much time you’ve “Accrued off-books”, because while they won’t pay you at termination for “unused but earned” time, they always expect you to pay back any time off taken that would exceed the same ‘limit’. Usually a contract is supposed to show benefit to both parties, to be considered valid. Unless you’ve bought a legislator or two, and gotten the law to except your underhanded scheme. Or operate in a state where someone else already did the hard work of getting the laws changed, and all you have to do is screw over your employees when the time is ‘right’.
There is no recourse from a bad manager. If you end up with a project that is poorly managed, when it comes down to it, no business is ever going to let you take the time off you’re owed, at the expense of day-to-day operations, so even if you manage to eventually get the bad manager out/reformed, it’s already too late, and the worker gets screwed.
Nothing in the prior time-off plan prevented a manager from granting exceptions to exceptional circumstances, so again, the whole point of this change is to give the employer more options, and the employee fewer.
But you get to sound all generous and say things like “unlimited time off” without technically engaging in fraud.
Update: Thought of another one….under normal time off, you just have to ask for it, and verify that your request won’t conflict with the business schedule. Now, you’ll have to explicitly justify every time you want to be out of the office. It’s none of your frackin business what I want to do when I’m not at work, and I sure as hell am not coming begging to you for what was once a contractual part of compensation.