Professionalism has the following effect, scaling up from 0 to 100:
- Shock Damage +10%
- Fire damage +10%
- Movement Speed +20%
Additionally, low professionalism grants bonuses for the recruitment of mercenaries, starting from 0 and scaling down to nothing at 50 Professionalism.
- Mercenary cost -15%
- Available mercenaries +15%
(...)
Abilities gained for each 20 Professionalism:
20 - Supply Depot Ability unlocked for army.
40 - Refill Garrison Ability unlocked for army
60 - Disbanded Units are returned to the manpower pool
80 - Military Generals cost half-price to recruit
100 - Your reserves take 50% less morale damage.
Supply Depot is an ability accessible in the revisited Unit view which, for a small MIL cost, established a depot in a province. Friendly supply in that entire area is increased by 50%. If the province is then occupied by a hostile force, the Depot will be destroyed, otherwise it lasts for 2 years.
Refill Garrison allows an army to take some of its manpower to restore the garrison of a fort instantly so you can proceed without having your new occupation snatched away.
Disbanded units are normally lost forever, however at 60 Professionalism you ensure that they return to the manpower pool
Half Price Generals cost is fairly self explanatory, they will cost 25MIL rather than the standard 50
Reserves, who normally take passive morale damage in large ongoing battles, will now take far less and can really turn the tide in a battle.