The level of information collection directly affects log sizes. Depending on the setting that you select, the logs can become quite large. By limiting the log level and collecting the information from a representative sample of users, you can decrease your log size and still have sufficient information for analysis.
For example, if you are debugging a test, you might set all three What to Log fields to All or Action Details. These settings produce large test logs, especially if your tests are long or you are running a large number of users. Large test logs, in turn, increase the test log transfer time, and might even cause your computer to run out of disk space. To reduce transfer times and the likelihood of running out of disk space, sample information from a very small subset of users; smaller even than the default of 5 users per user group. A fixed sampling rate samples the same number of virtual users from each group. A percentage sampling rate samples a percentage of virtual users from each group, but guarantees that at least one user is sampled from a group.
To set the amount of information collected in the test log and the rate of sampling:
Both choices, as well as the default setting, will limit the size of the test log and reduce the total time to run the schedule by significantly shortening the test log transfer time at the end of a test.