In many cases you will recieve a lot of loot during your explorations. If you have the space, you could lug it back to a station to sell it, but usually scrapping them is a lot faster. Later in the game, once you have items you would like to hang on to for a few levels, you might get the following problem: A lot of crafting material, but no cash, or vice versa!
Here is a simple thought to help you if you want to keep both flows going. This goes well for most items, but for weapons, also pay attention to the modslots. A maxed modslot weapon might be very interesting for another player, even if he has to buff it up himself.
Scrap them, all of them, they just take in space and will give only up to 100 Palladium The scraps might be used yourself or sold later, but atleast they will take in a lot less space.
Sell them if they are not of your class, scrap them if they are! This will allow you to get some cash, while also giving a good supply of the mats you need to upgrade. As soon as you start running out of space, scrap some greens, especially if it is to loot blues or betters. Don't identify them, even if you would sell them.
These you keep to sell. They give about double of a green item, so moneywise a good investment of your limited space. These will be worth identifying after about lvl 20.
If you would have to choose, I suggest selling, preferably to another player.
With the new patch, the "empty" uniques should be gone. Normal uniques are definately worth keeping for other players.
You will find many useless mods during you adventures. These are worth selling though. Even a white mod will give about double of a white item and takes only 1/4 or less of the space, making it eight times more efficient to sell.
Identifying: Only identify items of blue or better quality if you can wear them. Atleast up to lvl 30, identifying green items will be more expensive than it's gain in sell value.