Make videos smaller: lower resolution and quality. Ideal for emailing or uploading. Output: WebM.
Email is nearly always the limit: plenty of servers refuse attachments somewhere between ten and twenty-five megabytes, and your recipient's ceiling counts just as much as yours. At 720p and the default quality, reckon on roughly fifteen megabytes per minute of footage. A two-minute clip fits comfortably; a fifteen-minute recording never will, however far you pull the sliders back. When that happens, compressing a video for email is not the answer: send the original as a download link and keep the quality.
Maximum height does most of the work. Going from 1080p to 720p drops about half the pixels, and the file follows; 480p halves it again. The quality slider fine-tunes within that choice: around 55 ordinary footage still looks fine, while below 35 you notice it first in busy, moving scenes, which turn blocky. Only keep 1080p when there is small text on screen, such as a spreadsheet in a screen recording. And if nobody speaks in the clip, switch off 'Include audio' — that saves a little more.
The work happens in your own browser: the video is re-recorded while it plays. So allow roughly its running time, and leave the tab open. Nothing goes to a server — the file stays on your computer, which matters when there are client details or internal footage in it. What you get back is a WebM at 25 frames per second, so a smooth 60fps recording loses a little of that smoothness. It plays in any modern browser and in VLC, but if your recipient works in older software, check that before you send it.