A daily chart on a computer screen will comfortably show five or six months of history. You will see less with candlesticks, which take up more space. Daily charts alone are not enough, and you need weekly charts with at least two years worth of history. Learning history prepares you the future, and it could be helpful to glance at a 10-year chart and see whether that market is high or low in the long-term scheme of things.
Charts spanning 20 or more years are especially useful for futures traders. Futures, unlike stocks, have natural floors and ceilings. Those levels are not rigid, but before you buy or sell, try to find out whether you are closer to the floor or the ceiling.
The floor price of futures is their cost of production. When a market falls below that level, producers start quitting, supply falls, and prices rise. If there is a glut of sugar and its price on the world markets falls below what it costs to grow the stuff, major producers are going to start shutting down their operations. There are exceptions, such as when a desperately poor country try to sells commodities on the world markets to earn hard currency, while paying domestic workers with devalued local money. The price can dip below the cost of production, but it can not stay there for long.
