All coaxial cable has loss. That's when some of the transmitted or received signal is lost in the coaxial cable. This is normal and all cables have it. What varies is the amount of loss over a given distance.
Low end coax will have a lot of loss.
High end coax will have less loss.
If the loss gets to be too much, you'll lose most of the benefits of an external antenna.
Too much loss, and the weak signals picked up from far off stations by your antenna will be too weak by the time they make it down to the radio. But, you don't need to go overboard.
So, you'd need to look at the length of cable you'd need, and make a decision on how much signal you were willing to give up.
Antenna height makes a big difference. Since 2 meters is -mostly- line of sight, the higher your antenna is, the farther off the radio horizon is. This can be tricky since getting an antenna up high creates two issues:
1. the mechanical support - what's it attached to?
2. longer cable run, see the cable loss description above.
Different types of antennas have different properties. There are a number to chose from.
If all the stations/repeaters you want to use are in a single direction, you can get directional antennas that will send the majority of the signal in that direction. It also works the other way, directional antennas will pick up weaker signals better in one direction.
Omni directional antennas give you equal performance in all directions. This is usually your best choice.
Antennas come with different amounts of gain. Antenna designs can focus more of the transmitted power towards the horizon. This is a good option if you are out on the plains and the horizon is a long way off. On the flip side, if you are deep in the mountains, higher gain antennas that focus power at the horizon can be poor performers if the other station is well above or below you.
Also, higher gain antennas usually cost more.
So, from your other post, sounds like you are looking at a Chinese radio and a base antenna. That would be a good starting place based on your situation. You'd want a small diameter coax cable to connect between your hand held radio and the main coaxial cable. This is done to reduce stress on the radios antenna connector.
You'll need some decent coaxial cable running to the antenna. The exact type will depend on how long the run is. You can get effective performance from lower cost cable, so don't let that turn you off.
You'll need a way to support the antenna. A piece of conduit attached to your home will work. Old TV antenna mounts, lots of options out there.
You'll need an antenna designed for the frequencies you want to use. 2 meter band is 144MHz to 148MHz, and a basic vertical antenna will be $50 or so. You can also make your own pretty easily, but you'll need the materials and tools to do it. Not out of the question, and pretty easy to do.
With some careful work, I think you could get yourself a basic Chinese VHF radio, some coax and make a simple antenna for under $100 bucks.
The answer is a qualified yes. As everyone here has pointed out, it CAN help. But it isn't absolutely necessary. I know someone who stood on the beach in Tel Aviv with a hand-held radio and talked to another ham doing the same thing in Malta over 1000 miles away. Small portable radios don't have to limit your abilities. Being portable means you can take it to places like a sea shore where over-water ducts can send your signal to unbelievable distances. I was there when my friend Tony, N3JLI talked to someone in a tractor in Iowa using a 5/8 antenna from his boat on the Chesapeake Bay using only a couple watts on six meters.
That said, altitude is usually your friend. I happen to work at a place with line of sight paths to DC and Baltimore. An outside antenna with reasonably decent coaxial cable can do amazing things. HOWEVER, these radios aren't perfect. They were not designed with high signal environments in mind. If you take them to places with other high power operations, it will probably saturate the receiver and actually keep you from hearing those stations. This is called blocking.
You should be careful when operating near commercial antenna sites because your signal could actually carry a lot further than your ability to hear the replies. This is especially the case with wideband VHF and UHF radios. Talk to the stations you can hear.