A premium account provides:

• + 100% to army experience gain
• + 100% to squad experience gain
• + 100% to soldier experience gain
• +1 to the maximum number of infantry squads in the battle
• +1 to the maximum number of squads with vehicles in the battle
• The ability to keep more soldiers in reserve

Enlisted Gold - a premium currency, which can be spent in-game on Premium account, soldiers and weaponry, soldier training, squad and campaign level-up etc.

Note, that you can use the "Assaulter" squad soldiers on the second level of the corresponding campaign and add them into squads with available slots for this class.