Most investors buy and sell stocks far too often, and lose a lot of money as a result. Every time you buy or sell a stock you pay a brokerage commission. Even worse, when it comes time to do your taxes, you have to calculate profits on stocks you've sold and pay taxes on these profits. Selling stocks can be very expensive, and can cost hundreds of thousands, even millions, of dollars over the course of a lifetime. If you simply sell your stocks less often you can save a lot of money in brokerage expenses and taxes.
Many companies sell software packages that do portfolio accounting.
The NAIC has software you may want to look into, particularly if you are buying or selling stocks often. At tax time, you can take your portfolio spreadsheet to an accountant the club has selected. The accountant will give each investor a form called a K1 which computes the investor's tax liability. This K1 should be included with your tax return. The amount listed on the K1 should be added to your adjusted gross income when you compute your own taxes.