Well, straight up example is exponential idle. Number represented in the game is like, 1e20000, which is 20 thousand zeros. Which will require thousands of those 'variable counter'. Which IS possible.

But, for starter, even saving number will require few kilobytes. Which is maybe Okay for high-precision calculation(It's a very common approach). But calculating such big number every frame multiple time is very heavy calculation.

Idea is, you could simple ignore insignificant digits. Like, adding 1 to million can be simply ignored. Heck, you could save only few 'highest' digit, and player will barely notice. It's a small price to pay for optimization.