When money is tight, and TRN’s need to be loaded, ART/INF can increase your number of units to fill the trannies instead of transporting empty space.
Also, IPC for IPC, INF/ART is actually superior to INF/ARM. ARM/INF comes out ahead on defense, and of course ARM can move faster.
BUT… in a knock-down, drag out, where your trannies HAVE to be full to have as many units landing as possible, ART/INF can be a life saver.
The math for INF/ART vs INF/ARM:
For ease of calculation: 56 IPC’s spent total (over 2 rounds)
Buying INF/ART pairs:
8 pairs, 16 total units.
Buying INF/ARM pairs:
7 pairs, 14 total units.
Offensive punch:
8 pairs ART: 32
7 pairs ARM: 28
Defensive Power:
8 pairs ART: 32
7 pairs ARM: 35
So, if you are on offense, and need unit numbers, go ART/INF.
If likely to be on defense, or need speed, go ARM/INF to fill your trannies.