Students with a consistent study habit know that tens (or even hundreds) of words come due for review each day.
Some students (when they are about to enter a period of time when they will be unable to study at all) reach out and ask if there is a way to prevent their memory strength from getting weaker over time (in order to prevent the buildup of reviews due).
We have always pushed against this idea. Our SRS algorithm creates a model of which memories in your actual brain are weak and in need of review. The more accurate our model is to what is actually happening in your brain, the more efficient you will be when using Hack Chinese.
Although it's easy to "freeze" memories on Hack Chinese, we aren't able to do the same in your actual brain.
If we freeze your memory strength in Hack Chinese, we are distorting the model - making it less likely to feed you the optimal order of reviews that keep you at the efficient frontier (retaining strong memories and learning new words).
While it may feel good to see memories staying strong (and waiting longer than usual before you review), you are then more likely to forget -- and restart from scratch -- any individual word.
Having said that, when enough students request something, we give it more thought.
Although we still don't think freezing your memory strength is a good idea, there are benefits to being able to manage your SRS experience in a way that fits your life. As with Account Resets, the mathematically optimal way forward isn't always the "best" solution when designing software for humans.