This is a very useful tool which is a combined unit.
Use the voltage checker to check for live circuits when fault finding or doing repairs/replacements. Use the continuity checker for fault finding and also for checking fuses and checking light bulbs.
You can buy separate tools for doing this but I prefer a combined unit.
For live testing the probes are specially designed so that all but the very tips are insulated which help reduce the risk of shock or causing a short circuit when testing.