We personalise the recommendation to your portfolio taking into account the total portfolio size and cap the proportion of portfolio which should be withdrawn. This ensures that there are no sudden and dramatic moves.
Also, as you know, Portfolio Scan is a periodic process, so if some units are retained, they will be exited in the next round.
Why is a big change in portfolio to be avoided? This is because when you withdraw, the money will remain in your bank account until it’s picked up for reinvestment (upto 5 working days). During this time, the market could go up. This risk of being out of the market when it goes up (experts call it “out of market risk”!) can be minimised by making smaller changes over time.