My printer (well, PrusaSlicer) always starts with a line around the object I am printing. See (1) in the image. --Why? What does that do?
There is also this line (2) at the front of the bed. --Why? What does that do?
The 2 is a purge line, meant to clear any pressure in the nozzle and wipe it off before a print. It can be edited in your Start G-code on the printer settings tab > custom g-code on prusaslicer.
The 1 is a skirt, meant to get rid of any last few hanging bits of filament and start a clean print (sometimes the purge line doesn't get everything off the nozzle). It can also be used to gauge any last minute adjustments to your z offset. If the nozzle is too close or too far, you'll know before the print actually starts. I find that the skirt can be disabled if you're using a brim, since it's redundant at that point. Some who have fine tuned printers may opt not to use one at all without much issue. It isn't meant as any kind of draft shield as another person said - that's a separate setting. It's just a failsafe for the cleanest prints possible, avoiding hanging bits of filament, blobs from built up pressure, and incorrect z height. The first layer is the most important so everything that helps the first layer helps the rest.