CPC price model is unique in its own way - the number of clicks on your particular creative depends on creative's quality and how it fits within the targeting parameters (GEO, devices, type of traffic, category etc.).
It's merely impossible to predict the exact number of these interactions - that's where the prediction and reservation part comes in.
Our special algorithm based on machine learning takes into consideration all of the campaign's and creative's parameters and analyzes them. It then predicts with quite an accuracy how many clicks you will have on your offer and reserves the amount of money equivalent to these clicks.
It's important to note, that for some formats clicks can be delivered much later than the campaign has ended and your creative was impressed. So money is reserved in order for you to have a positive balance to pay for future, non-instant clicks. It's made mostly for you not go overdraft with your balance.
When clicks are registered (it happens each hour) - the amount of money reserved diminishes by the cost of this clicks as does your balance.
When all possible clicks are registered (for some formats it can take up to 48 hours) - there is no more reserved money - just your balance being diminished by the cost of all the clicks.