I was looking for SIP with a horizon of 10 to 15 yrs, so never thought about selling.
But if I have to sell, I will try to identify the period when both Broad-based indices and strategy based indices corrected. If we can identify such opportunities, we can increase returns by selling and buying again at a low price or increase the buying quantity during a correction.
In the chart above, we can see the Indices corrected in 2008, 2011, 2013, 2016, 2018 & now in 2020. So almost every two or three years, these Indices give correction when the gain is either negative or very low. These patterns can be identified and used to increase returns.
About ETF or MF, both have their pros and cons. As I believe in buying and selling, I always prefer ETFs. The tracking error and expense ratio can affect performance of an ETF against index fund. But I can compensate that by selling when correction is anticipated and Buying again/more at lower levels.