MySQL server Load depends on Query you are executing.
If limit is set to 50 then “Select Query will be appended by limit clause”
and
If you are viewing all records of a large table then it depends on MySQL server performance, Number of records, Datatypes used etc..
Also if you have selected “ALL rows” option by mistake, there is a STOP button on toolbar to stop retrieval of records.
i.e. You can click on STOP button if you do not want to retrieve all records of a large table OR you want to move to limit.