Most people use special repayments only inadequately. Often not even for vacation or leisure.
In the beginning, there is still quite a bit left. First the garage (first special repayment gone), then the outdoor area is supposed to be finished at some point —> also in year 2 and 3 no special repayment. Then the children come and need the initial equipment or turn 6 and need school supplies. The year was already so expensive anyway. Then unexpectedly the need for a new car arises, and in the first 10 years you have only made 1-2 special repayments. After 15 years, the interest rate is then half a percent higher and you have practically paid off nothing by then. In addition, you might also renovate a room again, the old bedroom and living room furniture have also had many years, etc.
Of course, you can do it differently, but with just 1% repayment it is hard for me to believe that you regularly add another 1.5-2% every year. In addition, you usually pay for the low repayment rate and the high special repayment right with a higher interest rate. So you pay quite a bit for flexibility.
Many banks offer 1-2 adjustments of the repayment rate during the term. Often one is enough if you then maybe top up the remaining money later again through special repayment.