There is a line at top right corner
71.12% of Total sessions
What does above line means to the data?
What about the remaining 28.88%?
It's sampling. Google Analytics analyzes a sample set of data to extrapolate an estimate of 100% for certain non-default reports. This is common with most analytics tools as it saves huge amounts of space / CPU.
The thresholds for Google Analytics are thus:
Default reports are not subject to sampling.
Ad-hoc queries of your data are subject to the following general thresholds for sampling:
It is possible to get un-sampled data using the API but for most purposes, sampled data will still allow you to make actionable marketing decisions.