Totally agree, coinmarketcap will help to find important information for proper coin choice for trading and investment, I had experience checking one of the coins which decreased in volume above %50, so I decided to sell before the price was dumped in the market.
That is what such site are for, if you want to know information about a certain coin, just go and check about this on coinmarketcap, if I do not see the coin on coinmarketcap, I will not buy it. If I see the coin on coinmarketcap, I will still check the exchanges it is trading, I like to go for the ones with high trading volume, the trading volume is listed also along. But I have now prefer to just go for high marketcap coins, if a coin is not among the first 100 cryptocurrencies, I do not deal with the coin.