It is designed to smooth out the impact of business cycles and defined as price divided by the average of ten years of earnings, adjusted for inflation. So, we can think of it as a long term PE, mostly applicable to cyclical businesses. Here are more info:https://en.wikipedia.org/wiki/Cyclically_adjusted_price-to-earnings_ratio
If you apply Shiller PE ratio to indexes, such as S&P 500, you may estimate “how market is doing” and I think this I what Phil Town is talking about.
You may argue that all businesses are cyclical to some degree and therefore this ratio can be computed per individual stock. No disagreement here. However, if your plan is to hold a stock for 10+ years, you should count for inflation level change as well and expect to see at least one pull back of 20+% on a market, because market itself is cyclical. Can you use Shiller PE to spot next market top or bottom? Maybe.
Here is a chart of average earnings of S&P 500:https://www.macrotrends.net/1324/s-p-500-earnings-history
And here is Shiller PE ratio chart:https://www.multpl.com/shiller-pe
Currently, it is not as high as in 2000, but it is been above 15 since late 90s and the trend is up, meaning that market expectation for earnings growth is still high and any under delivery may cause market correction, just like we saw in December of last year.
For individual stocks though there are several other ratios available that are doing somewhat similar. For instance, PEG ratio takes into account earnings growth rates. We all know how important growth rates are and keeping an eye on PEG is beneficial.
Another way to think about stock performance vs inflation is to use Sharpe ratio. The Sharpe Ratio compares stock performance with a "risk-free interest rate". It means that Sharpe Ratio will be negative when stock performance is lower than defined risk-free rate. In practice, a risk-free bond is usually chosen - that is, one issued by a government or agency whose risks of default are so low as to be negligible. Stock2own uses a constant 5% as a risk-free rate of interest.https://www.stock2own.com/StockMarket/Theory/FundamentalAnalysis/Ratios
Sharpe Ratio as well as PEG and PEGY ratios are available in Stock Analyzer page.