If an MTS unit can only supply 5 Amps and your locos pull 1 amp each under load then you can have five running in each section, if it's a loco shed you may well have five sitting on shed and two moving which is fine as the stationary ones are probably only drawing 0.2 amps each to power lights and sound.
So for a large layout with say 3 big stations and 4 single track sections between them you might make all 4 single track sections actually powered off one booster, (assuming max one train in each section), while each station has a separate booster due to more power being drawn in those sections.
Alternately you might make one it one station and one single track section powered off one booster but that one extra train on the single line may be enough to overload the station section.
The main thing is that each section needs insulating rail joiners in both rails at each end to fully separate it from the next power wise.