There are a couple of primary factors here...
First and the biggest is the exposure of running some fairly large wire across a fairly large distance. The risk of shorts of course increases as you go further. This can be mitigated by appropriate fuse or circuit breaker protection.
Next are the connections that are typically needed. More connections mean more potential failure points for a critical element in the electrical system. This especially becomes true as current flows are increased, which a 10g wire can support, but see below.
And finally the voltage drop which may result from the extended power feed wiring. Now this one may not be quite as big a deal as many make it out to be. If set up right, during normal operation this wire may carry very little current at all. And that will go a long way to minimizing voltage drop.
An interesting debate could be had on the relative merits of the diagnostic capabilities provided by an ammeter versus a voltmeter. For a basic charging system go/nogo test both function just fine. And then they diverge...
An ammeter tells you if and how much current is flowing into or out of the battery. This in turn tells you if the battery is charging as expected or discharging. Discharging would indicate no or low alternator output and send you to the garage. Further knowing the amount of flow better allows you to manage the battery capacity when failure occurs. Turning off devices is visible and the amount of flow provides some rough idea how long the battery power may last.
A voltmeter tells you how high the voltage is in the system. Which can actually tell you quite a bit IF you understand how things work. The battery normally provides somewhere around 12.5v when fully charged and this voltage drops as the battery becomes discharged. The alternator, through the magic of the regulator, normally provides around 14v. Thus you can deduce that at voltages above 13v the battery will be charged and below 12.5 the battery will start to discharge. But you can also tell if the regulator fails and allows the alternator lock on and raise voltage too high. This can be bad for battery life as well as other electrical devices. You cannot tell this from an ammeter. And if you understand the voltage drop versus battery charge, you can estimate remaining battery charge too.