I realized that most finance and stock screener web sites don't provide the metric of the mean (average) price of the stock over a certain period of time, for example, the mean value of AAPL shares over the last 12 months (which I computed to be around $117 from 2015-02-20 to 2016-02-19). Is there a reason for this? Is this metric useless?
Edit3: Regarding the usefulness of the bare number itself, it is not useful unless, for example, an employer uses that average in the computation of how many options the employer grants to the employee as part of the compensation paid. One of my employers used just such an average. What is far more common is to use two or more moving averages, of different periods, plotted on a chart.
My original response continues below...
Assuming there are 252 trading days a year, the following chart does what you have done but with a moving average:
Edit: BTW, I looked up the number of Federal holidays, there are 9. The average year has 365.2422 days. 365.2422 × 5/7 = 260.8873. Subtract 9 and you get 251.8873 trading days in the average year. So 252 is a better number for the SMA than 250 if you want to average a year.
Edit2: Here is the same chart with more than one average included:
That metric is not very useful for anything other than very extremely long trading periods.
Most strategies or concerned with price movement over much shorter time frames, 15 mins, 1 hr, 4 hr, daily, weekly, monthly.
The MA or moving average is a trend following lagging indicator used to smooth out price fluctuations and more accurately reflect the price of trading instrument such as a stock (AAPL), commodity, or currency pair.
Traders are generally concerned with current market trends and price action of the instrument they are trading.
As such, an extremely long MA (average daily price, over a period of 365 days) are generally not that important.
I would have to disagree with the other responders. In technical analysis of stock charts, various short and long term moving averages are used to give an indication of the trend of the stock in the short and long term, as compared to the current price.
I would prefer to use the term moving average (MA) rather than average as the MA is recalculated every day (or at appropriate frequencies for your data) on the period you are using. I would also expand on the term "moving average". There are two that are commonly used
Going back to the question, of the value of this number, For example if the current price is above the 200 day EWMA and also above the 30 day EWMA, then the stock is broadly trending upwards. Conversely if current price is below the 200 day EWMA and also below the 30 day EWMA, then the stock is broadly trending downwards. These numbers are chosen on the basis of the market you are trading in, the volatility and other factors.
For another example of how a number of moving averages are used together, please have a read of Daryl Guppy's Multiple Moving Average, though this does not use moving averages as large as 200 days.