Start with a small 2 car garage (300 SqFt) and it goes up from there. Almost all club size layouts are larger than 300 SqFt. Large layouts tend to need:
1) long bus runs (Cab Bus, Booster/Control Bus and Track Bus)
2) more power (current) to run more trains.
3) power management using "DCC Circuit Breakers" to create "Power Districts" to control short circuit issues.
4) a Track Bus with large gauge wire to carry the high current over long distances with minimal voltage drop.
Such layouts can start to have track bus wire runs longer than 30Ft which is the beginning point at which problems can start to appear. Clearly there are those that claim they have long bus runs and have no problems. The problem with such statements are:
1) Each Layout is wired differently. The quality of the wire and installation will vary greatly along with the routing and bundling (intentional or not) of various wires together. It is as unique as the individual who built it.
2) Most people do NOT know what to look for in terms of potential electrical problems. If it runs, it must be OK....wrong.