Defensively, it could make it annoying for enemies to attack you with armored vehicles.
No. It woud be even
more comical easier to fight your enemies in high gravity. In low gravity your enemies may survive a landslide by hiding in a tent. In jovian gravity a paintball falling from a few kilometers up could maybe rip a person right in two.
If you wish to fight someone in high gravity, warfare may become a game of dropping stuff up on your opponents.
That said, the pains of high-gravity are:
More expensive life support: we know humans handle low gravity, and even microgravity quite well. People are able to live for months in the ISS without any major, long lasting health issues. But we feel sick and can get knocked out by high gravity, as evidenced from simple things like some ******* rollercoasters to more complicated stuff such as jet fighters and rockets (in some cases you need special suits just not to pass out).
The energy bill: the real issue is that the formula for the potential energy of a gravity field goes like this:
$$ E = Mgh $$
Where M is the mass of a body and h is how high it is from a reference height. The problem is the g, which is the gravity involved.
Let's compare three hypothetical planets, with distinct masses. Let's call them planets A, B anc C. Let A have the mass of Enceladus, B have the mass of Earth and C have the mass of Jupiter.
If you are in a building and wish to take some load to another level that is 10 meters upwards, the energy cost will be different in each. Assuming that the load weights one metric ton, the energy cost for each planet would be:
Planet A: $ 10^3kg \times 10m \times 0.0113m/s^2 = 113 \space joules $
Planet B: $ 10^3kg \times 10m \times 9.8m/s^2 = 98,000 \space joules $
Planet C: $ 10^3kg \times 10m \times 24.79m/s^2 = 247,900 \space joules $
If you have a power supply unit that can only power one elevator in a jovian gravity, the same PSU will be able to power two elevators simultaneously on Earth, or up to 2,193 elevators on Enceladus at the same time.
Conversely, a 10 meters drop in each planet would mean an impact with just as much kinect energy. In planet A you could jump from a hill and land like a feather. In planet B you could jump just like on Earth. On Planet C you risk serious injury and even death if you just trip on the sidewalk.