The sample rate is defined via a random sample of users.
For example, let’s say you are trialing session replay and you have 10,000 sessions to sample from. Assuming on average a user has one session per day, and you have 10k users a day, then setting the sample rate to 100% will use up your sample rate quota in a single day. If you set your sample rate to 10%, then you will use up your quota over 10 days.
Note that spikes in traffic may impact these estimates.