What are freighters for?

Transport. You can transport colonists, satelites, mines etc... To name just a few.

Groovy Baby Yeah!

You use your freighters to transport any: population,satalites,troops,mines,fighters,weaponPlatforms from one planet to another?

They can also be used as fleet Auxilleries carrying ammunitions and supplys for the fleet?

And last but by no means least you can at a push use it as a large warship early on in the game, as it has lots of free hits (cargo boxes) to absorbe damage?

Hope this helps Spuda

and they are realy great small carriers...

They make fantastic non-combat minelayers/satallite layers/fighter launchers as all three of those only recquire a single launcher (though usually you'd need a combat launching carrier).

Much more space to fit in those mines/satallites/fighters.

I agree! As soon as mines/sat are researched they are great early multi purpose ships but should include good (lvl 3) sensors.

A small freighter can take roughly 15 population, 50 small mines or 20-30 fighters.

As soon as possible I load them with mines and follow the scouts/colonizers to mine critical junctions/system warp points or to seal of known other empires, or deply sensor sats for early warning.

10-20 mines are good early defenses and can be build like fighters in every colony.
Resupply at remotest colony and act as scout.

Otherwise I use them as population transports or as armed (fighters!) scouts (sensors lvl 3). The sensors dicover the stray enemy scout/colonizer, launch fighters and destroym, mining WPs as they go, mine possible colony sites. They also make good fleet auxilaries early on. (Jeep fighter carrier to replenish fleet carriers/boarder colonies, supply ships)

Can also make a passable auxilary warship/convoy escort early
(As a historical note, England did much the same in WW2 in using bulk freighters as every cargo ship was needed. Slap a flight deck on the bulk(grain, coal, liquid) freighter and you get an extremly useful instant escort carrier without losing cargo space.)

Retrofit with a mounted gun and think commerce/colony raider in a war situation, mining behind enemy lines can be fun or load supplies/fighters for long range harrasment. Cheap and expandable in war. Useful in peace.

But what are the benefits of freighters over carriers or warships? I use my frigates and destroyers during the early part of the game to act as my resupply ships and light carriers. I do use the freighter as a population/satellite transport, but I only need 2 or 3 of these.

"We are the Vahl, resistance is...welcomed"

there's no benefit for freighters over carriers. they are mostly non-combat ships, though you can fit them with armour and guns.
they are supposed to augment your combat ships.
my freighters almost never leave my controlled systems. i use them for population distribution, mine laying, sensor grids, moving fighter groups from system to system.
the only freighters that end up in combat are my supply frieghters (Balance mod) that accompany my fleets.
in stock though.. they never leave controlled systems.

Maintenance cost and size. Frigates and destroyers tend to be too small, carriers too big.