This idea came to me in a match when me and my opponent (both silver leaguers for now) were camping in each of our own bases each waiting for the other to attack.
The advice sounds pretty obvious at first but one may be tempted to just focus on macroing up and leave his/her units near their own buildings. Yet all the professionals seem to be always attacking. Why would this be more effective?
Don't we have at least equal chances, leaving our army at home? Or better yet, maybe it is optimal not to attack ourselves so we have more concentration to focus on the enemy in case he attacks us.
Ok, first of all, in order to win, one must have an army, otherwise the opponent's buildings can't be destroyed. You can also win by the other player resigning but that is not in your power. The perfect opponent does not resign.
This means that, in case you want to win, at least one probe should not be gathering minerals or one must have built at least one pure army unit. To win at least one unit should be ordered to attack. That unit can be either a part of your army, or your entire army. Suppose it is only a part of your army. Then you have a fighting unit that is not attacking at the deciding tick. Then it is impossible for that unit to contribute to you winning. So that unit should not have been built, saving you some APM (That APM could give you extra energy for other matches in case it is significant). So your entire army is attacking at the time you win. Maybe I'm indeed overthinking, so I'll leave it at this for now...Greets
From previous version of this post:
A part of your army attacking has less chance to win than in case it was you attack with your entire army (strong army defeats weak army). So having units that aren't ordered to attack is a losing strategy.
So lets suppose that the "ultimate" strategy has a army/economy ratio of 5%.
(5% of units are fighting units). On top of that, one cannot win without ordering that army to move towards the enemy and to attack that enemy.
Second, since a bigger army has more chance to win, one needs to always be increasing their total empire size as opposed to going for a stable or decreasing empire.
Third, a unit, when ordered to attack at an earlier time, outperforms that same unit when ordered to attack at a later time. If we assume exponential empire growth, an army of 5 units can be for example 100% of your total army at 120 s and only 10% at 180 s. So by the time your army arrives at 180 sec it is only 10% of the size of your enemy's army (who also uses perfect play).
Since an army consists of individual units that each are better when ordered to attack at an earlier time, it is better to send units continuously as opposed to discreetly.
Fourth an attacking unit that does not attack sets you behind because you could've built a worker unit instead.
Therefor, since a part of your units are attacking units, they should be moved towards the enemy. Maybe that's what Tasteless refers to as "playing against the game" as opposed to only playing against the opponent?
Note: if the enemy is in your base, moving means ordering them to go in attacking range of the enemy units in your own base.