I have designed my company to provide me with all my required resources except ads. I had a great supplier of ads but I filled my stores now so I don't buy ads anymore.
I produce some expansion products as well as other factories products which I then sell in my retail stores for caps. This strategy is meant to supply me with expansion products and caps enabling me to expand my company without relying on market prices.
When I expand I don't want to expand all my buildings by 10qm. I want to expand them by at least 100qm at a time. The number of expansions you can do per day will increase slowly as I expand everything, however..
I normally start expanding my mines, wells and power plants first so I don't have to buy required products from the market when I expand the factories. This leads to an over supply of some resources.
So sometimes I need coal or oil, other times I need steel or plastic, and other times I just need caps. A Trade Syndicate is another great place to find contract buyers and sellers other than the sales market, faxes or game forum.
A Trade Syndicate is also a great place to find long term suppliers and customers for my redundant products which I have stopped producing because of a quality increase. Although I don't normally over produce enough to warrant the trouble and find I normally sell redundant products on the sales market.
There are a few other valid reasons to be in a TS (ie. an extra forum to read
