Another option when you register your domain names will be to setup for auto-renewal.  This allows the domain registrar to try an auto renew your domain names against the credit card you used to pay for the domain names originally after the initial 1 year term is expired.  This can be very helpful or a real pain it all depends on what your trying to accomplish.

If your goal is to buy and sell domain names you probably don't want this feature turned on.  Your goal should be to "flip" (sell) 70% of your domain names each year and buy new ones so the renewal is more of a waste of time.  The downside is you have to keep good track of what domain names are coming up for renewal if you haven't sold them and decide if you want to keep them or let them drop.  Now your domain registrar should provide you with warnings before the domain name comes up for renewal, but with a large domain name portfolio you may miss it.

If your goal is to purchase a domain name for your company or to develop it can be a great feature.  First you don't have to worry about when it's going to come up for renewal they magically charge your card and you have the domain name for another year.  Just be sure you have room on the credit cards you are using and that the credit card doesn't expire.

If your goals is mixture of the tool you have to way the options.  Is it more important to keep the domains or watch the cash flow and do your best to catch the domains before they renew.  You may be forced into this option if you have tight cash flow.  A hundred domain names renewing in one month can really add up.