The momentum effect is that if the bitcoin price rises continuously over a week, it may keep growing for the next week. This is a common feature of almost all known asset classes, and we have found that the momentum effect strongly affects the cryptocurrency. We have designed a simple investment strategy in which investors buy Bitcoin only when their price increases by more than 20% from the previous week. This strategy has excellent returns and a very high Sharpe ratio. 
I don't think I will advice any investor to buy bitcoin when the price is high. You need to check and know the consistency of a particular price or prices of Bitcoin at that moment in time. People just invest in Bitcoin because of speculations they hear with regards to the possible profits they can make within few weeks. It is a bad idea to buy when the price is high, what if after buying the price declines at a particular rate? Meaning you find yourself investing wrongly.When price move more than 10% on bitcoin, investor prefer wait and see. Price movement more than 10% in bitcoin more affecting than altcoin because bitcoin is biggest market cap value in crypto market.