I have recently observed no matter how good your TA is, it doesn't always work on alt cos most alt price direction is impacted by BTC price.
When BTC is up all other coin move up. So why spending time on doing technical analysis on alts when doing it on BTC gives you a potential clue of most assets price direction?
Most time it plays out well but sometimes trade can go south if you ignore analysis on particular alt you wanna trade. So my advise is analyze both to be a bit safe