Of the ten most important reasons kids chose to play a sport, having fun was number one. For those who dropped out of a particular sport, the number one thing those kids said would get them re-involved in the sport they dropped was if practice was more fun (boys & girls).
Games are an alternate modality to generic drills and generic training methods such as interval sprints. Such drills do not offer the same motivation or enjoyment for players. Certain players are also engaged best through the competitive elements of certain games.
Players that are not skilled enough to get all of the "glory" of scoring goals in League play, get the chance to demonstrate their unique skills and feel a better sense of self-efficacy. Further, using a Move-Think-Learn Philosophy, using games is a great way to help kids internalize concepts being taught in drills.
Coaches are free to be creative and involve games anywhere within their Practice Plans, as long as there is a purpose that is served (any drill can be transformed into a game in some capacity). The reason could be as simple as to add some fun to the practice, to emphasize a particular skill, or to disguise a cardio-effect embedded in a game.
SSG ("Small-Sided Games") develop the physical, technical and tactical components of lacrosse, in conjunction with each other rather than in isolation. Manipulating the size of the playing area, number of players (which greatly effects intensity), shift duration, number of shifts, technical/tactical considerations, exercise type and coach encouragement, have all been shown to significantly alter the physical and technical demands associated with SSG's.
It is of paramount importance that practice design and SSG implementation should be performed with precision and careful consideration of the training objective. SSG's should simulate the physiological workloads and intensities commensurate of actual game play (1:2 work:rest ratio) while also developing technical and tactical proficiency. In practical terms, this could mean 30 second shifts with 60 second rests; or it could mean 3 players per line/tea during a "relay race" (i.e. 1 player working and 2 players resting).
SSG have shown cardiovascular stress and training adaptations comparative to generic short duration intermittent running training, with similar effects as 6 and 12 weeks of interval training in youth players during the competitive season (in soccer). It has also had a positive effect on both the anaerobic and aerobic system during in-season breaks (where no games were scheduled). That said, games should still be closely monitored to prevent players from overreaching/over-training.
There are many more goal attempts encountered during a 3-a-side game and many more ball contacts overall during a SSG. The ability to perform technical and tactical requirements under fatigued conditions should also be considered vitally important to team success.
An over-reliance on this training method may mask specific weaknesses within an individual player's profile and requires stringent control and standardization of influential factors.