If you are dealing with the big boys (argos etc) they wont look at your product unless the margin is 40% plus.
Argos won't even talk to you, you are small fry (no offence). You have to sell to their distributor who sells into them.
If you want above average space (larger than a postage stamp!) in their catalogue, basically you have to pay (lots). If you advertise your product elsewhere they may also have 'an influence' how you promote and price your product. Some companies will not even put your product in their catalogue unless you pay for the space! TV shopping chanels are the same. You pay for slots how many you want.
If they have similar products you have to tender/bid to sell to them (securing them a rock bottom price!)
They work 6 months ahead producing their catalogues. For instance you would be selling in to them now for the all important Christmas catalogue. Oh and be prepared to part with some 'marketing funds'

However as you are working so far in advance you can plan the production and finance. You essentially receive an L/C from them which if necessary you can borrow from a bank against (not recommended personally).
Large retailers can bankrupt you overnight unless you know exactly what you are doing, be warned. You have to know what you are doing and have a nice large cash flow.
Finally, unless you have sold in to them before just getting a foot anywhere near their door is impossible (unless you are Sony, Apple, Panasonic etc).
So in summary, it does have many advantages but it is not easy and you have to be able to back it up financially.