My spreadsheets give me background information for analyzing stocks. They give me information to analyze how a stock is doing and a basis to help decide what is a good relative price for a stock. The past may not be the future, but neither are the future and the past totally divorced from each other.
One of the things I get from spreadsheets is the answer to the question "Is the company growing?" I look at revenues, earnings, dividends, cash flow and book value. Revenue growth is important as without growth you are not going to get long term growth in earnings, dividends, cash flow or book value.
My spreadsheets give me not only current values and ratios, but where the stock has been in the past, for example on things like debt ratios. I can see how the stock is fairing relatively to what it did in the past.
Take debt ratios, a lot of sites will give you what it is currently, but you need the past to make sense of it, but you also need have a general knowledge where the debt ratios should be for the type of stock you are analyzing. Some stocks types of stocks, i.e. utilities have much heavier debt loads than other types of stock. This is just the way these companies operate.
There is another aspect of my spreadsheets. They contain a number of ratios, not only debt ratios, but things like Price/Sales Ratio, Price/Graham Price Ratio, Price/Earnings Ratio, Price/Cash Flow Ratio, Price/Book Value Ratio and Earnings per Share/Cash Flow Ratio.
They also contain current and historical yields, like Earnings Yield, Dividend yields. I include returns on assets, comprehensive income and net income or earnings.
When I look at the current stock price, I can perform a number of tests to see if the current price is relatively low or high. Usually I test price using Price/Earnings Ratios, Price/Graham Price Ratios, Price/Book Value Ratios and dividend yield. If these tests are invalid for any reason, I can also look at Price/Sales Ratios and Price/Cash Flow Ratios.
My spreadsheets one tool I use to analysts stocks. For such things like these ratios you need also to understand what is a generally considered to be reasonable ratios, which sometimes can vary a lot from relative ratios.