Mechanical sewing machines are the simplest machines that run on electricity. Most functions of a manual must be adjusted by you, the sewer. You control the speed via a mechanized foot pedal. Less pressure on the pedal slows down the stitching speed, while more pressure increases the speed.
This type of machine often requires the sewer to employ much more of a trial-and-error process than when making projects with other, more complicated, machines; thus, using a mechanical machine is often more time-consuming and not as precise regarding size and tension of stitches. Finding the correct tension for the project is vital since the wrong thread tension will make the stitches so loose that they will not hold or too tight so that the fabric bunches.
If shopping for a beginner or someone who will not use their machine often, a mechanical machine is the ideal choice. Their functions are easier to learn, and they are usually much less expensive than more elaborate machines.