The main advantage is convenience. Online editors are useful when you’re away from your usual computer or editing software and need to make quick, simple fixes to already-uploaded images. Based on the answers, common uses are cropping, correcting white balance or color casts, and basic levels adjustments—especially for phone photos shared to services like Flickr or SmugMug.

They’re also attractive because they’re easy to access and often integrated with hosting/sharing sites, so you can edit without downloading files or launching full desktop software.

The tradeoff is quality and capability. Web-based editors are generally slower and less powerful than native desktop tools, and at least some free services may save JPEGs with stronger compression, which can reduce image quality. For that reason, they’re best for quick tweaks rather than serious post-processing.

A good practice is to save the edited version as a new file and keep the original untouched.