What it does is accessing your webpage, clicking links, filling out forms and checking on the results (URL, Status Codes, etc.). I just implemented it for checking all of our stores checkout processes once a day.
Setting up is straigt forward and easy (as long as you have a check left in your Pingdom account). The Check editor offers context sensitive suggestions on actions and validations and has instant feedback on how long it took to perform the action and wether it was successful or not.
So with the Transaction Monitor annyoing repetitive task can be automated and thanks to that performed even more often as when executed manually.
For some inexplicable reason however there is an artificial limit on the number of steps you can add to a check which is currently 25 and limits the usefulness unnecessarily.