When mice still used a mechanical design (with slotted 'chopper' wheels interrupting a beam of light to measure rotation), trackballs had the advantage of being in contact with the user's hand, which is generally cleaner than the desk or mousepad and doesn't drag lint into the chopper wheels. The late 1990s advent of scroll wheels, and the replacement of mouseballs by direct optical tracking, put trackballs at a disadvantage and forced them to retreat into niches where their distinctive merits remained important. Most trackballs now have direct optical tracking which follows dots on the ball. Some mice, in place of a scroll wheel, acquired a small trackball between the buttons, useful in maps and other circumstances calling for scrolling in two dimensions.
Trackballs have appeared in computer and video games, particularly early arcade games (see a List of trackball arcade games) notably Atari's Centipede and Missile Command. "Football", by Atari, was the first arcade game to use a trackball, released in 1978 - though Atari spells it "trak-ball". Console trackballs, once common in the early 1980s, are now fairly uncommon: the Atari 2600 and 5200 consoles had one as an optional peripheral, with a joystick as standard. The Bandai Atmark, a Japanese console introduced in 1995 had a trackball as standard for its gamepad. Trackballs are also preferred by many so-called professional gamers, who value their consistency highly. A trackball requires no mousepad and enables the player to aim swiftly (in first person shooters). Trackballs remain in use in pub golf machines (such as Golden Tee) to simulate swinging the club.
People with a mobility impairment use trackballs as an assistive technology input device. Access to an alternative pointing device has become even more important for them with the dominance of graphically-oriented operating systems. There are many alternative systems to be considered. The control surface of a trackball is easier to manipulate and the buttons can be activated without affecting the pointer position.
Trackball users also often state that they are not limited to using the device on a flat desk surface. Trackballs can be used whilst browsing a laptop in bed, or wirelessly from an armchair to a PC playing a movie.
Trackballs are generally either symmetrical in design, with the ball operated by the fingers, or asymmetrical, with the ball operated by the thumb. Many users favour one format or another, for reasons of comfort, precision, or because it reduces strain on one part of the hand/wrist. Only the symmetric format can be used by both hands. Asymmetric or "handed" trackballs are not generally available in left-handed configurations, due to small demand.
Some computer users prefer a trackball over the more common mouse for ergonomic reasons. There doesn't seem to be conclusive evidence of one being better than the other in terms of comfort. Users are encouraged to test different devices, and to maintain proper posture and scheduled breaks for comfort. Some disabled users find trackballs easier since they only have to move their thumb relative to their hand, instead of moving the whole hand, while others incur unacceptable fatigue of the thumb. Elderly people sometimes have difficulty holding a mouse still while double-clicking; the trackball allows them to let go of the cursor while using the button.
At times when a user is browsing menus or websites rather than typing, it is also possible to hold a trackball in the right hand like a television remote control, operating the ball with the right thumb and pressing the buttons with the left thumb, thus giving the fingers a rest.