Companions are a big deal in Neverwinter. They are not just there to keep you company, they can actually really give your character a considerable boost. They can act as a permanent party member and they also give you some really good bonus abilities or stats, depending on which companion you get.
You are allowed five active companions in Neverwinter when you hit Max Level. You may, of course, take as many companions as your Idle Companions inventory allows (it is basically a separate bag, it is possible to expand this, but it is very rare that you will ever need that many idle companions). But, only the bonuses of the active companions will be applied to your character.