Victor: There is no straight answer on this question. This is a grey area. You will see different opinions from different analysts. By following common sense, when it comes to long-term trend analysis, we may say that you may use long-term technical analysis to define current trend on stocks and indexes – no doubt about that.
You may assume that the current trend will continue if nothing that may change a trend comes around. This would be considered as using technical analysis to predict future development of a long-term trend. However, long-term trend is long period of time and over that time a lot may occur. When it comes to stocks: we have quarterly and yearly reports, we may see changes in the ownership (company could be acquired, divided), we may see changes in the board of directors and top management of a corporation, there could be law suits, there could be new innovations and etc.
To say you could relay solely on technical analysis in stocks long-term trend would be wrong. Yes, you can use it, however, you have to monitor and analyze the fundamentals as well.
When it comes to the market analysis as a whole – analysis of the market indexes, it is a little bit different story. Market indexes are already passed some fundamental analysis. Companies calculating indexes, constantly monitor fundamental data and remove stocks which do not fit to be listed in an index by adding other more suitable for it. Yes, you still have to monitor, economical and political situation, however, here, long-term technical analysis could be more effective, especially if you add volume and Breadth analysis to price analysis.
Technical analysis can be used for any time frame BUT just technical analysis alone is not enough. In today's complex market and changing global information landscape, no one piece of information or news or indicator tells the whole story anymore. There is no such thing as a magic indicator or something that happens which will definitely lead to something. That's not how today's complex market work anymore. You would need a comprehensive top-down analysis approach going from how the overall market is and is expected to behave to the specific industry and then interprete this "indicator" in the context of that overall market and industrial background in order to arrive at a high probability conclusion. Yes, it is not an easy thing to do and why professionals like myself spend so much time in college and still do not get it down 100%. Good news is, you don't need 100% to win. Also, depending on what you mean by "long term"… if you are buying and holding for like 5 to 10 years or even 20 years, you pretty much don't need any analysis… just buy a market ETF like QQQ, SPY or DIA after a market crash and then hold for the long term… easiest way ever.
Short term technical analysis may be used to tell when to get in or out if it starts falling apart, but the average time periods for indicators once you are in would be longer term, so you are not so much influenced by relatively small pullbacks as long as the long term trend is up. And it helps if the company is financially sound (decent fundamentals).