You are forced to take vacations. What you do with them is beyond your employer's control.

I'm not forced to take vacations in Germany by my employer (large research institution). They roll over for a year, but then expire.

You are forced by law to take at least two consecutive weeks once a year. But yes my employer also allowed this and one of my colleagues had accumulated an absurd amount. You still had to take two weeks but could keep the rest.

As long as the relationship with the employer is fine, none.