As in a real football team, the goalkeeper in goalunited is a very important player and can be the deciding factor in a match.
Goalkeeping takes on a special role in training. It is the only skill that is not available as the main skill to be trained in the normal training programs. It can be trained as a second skill in the main training programs, or alone in general training. The training effect of goalkeeping training is slightly higher than the effect for the other positions.
While you can have 7 players on all the field positions without penalty, you can only have 3 goalkeepers without a significant penalty in training. You can however purchase a Keeper, Striker, Defender, Playmaker or Winger plus stadium upgrades and increase training positions by +1 for each of the positions.
Many teams choose not to train goalkeepers, but to buy good goalkeepers on the transfer market, even though they come with a hefty price tag. It is not advised though to have only one goalkeeper in your team. Even your goalkeeper can get injured or receive a red card, and in that case, you are in bad shape without a backup. The goalkeeping skills of your field players are usually very bad, and on top of that, they receive a penalty for playing on the wrong position (unless a repositioning card is played).
There are 3 Talents that only goalkeepers have. (Or those, that started out as goalkeepers.) "Penalty saver", "incredible reflexes" and "field player". As each one of those talents has a good chance of preventing a goal when it triggers, it is always good to have goalkeepers with talents.