sma is fine for small, light antennas, , but you cannot connect regular coax to it very easily without putting a lot of strain on the connector or using a very thin coax and adapters. Using adapters can be the cause of poor connections and signal loss.
...Using adapters can be the cause of poor connections and signal loss.
The real issue is if a heavy cable type such as LMR400 is adapted directly to an SMA connector, the weight and stiffness of the cable could damage the SMA connector on the radio. .