I'm by no mean a professional trader or something. But I'm quite good in statistics and math because of my engineering profession.
Anyway I will describe to you moving SL to BE is quite awful and noobish in few straightforward words w/o utilizing complex math.
1-You open two lots , with both TP 30 pips. 1 hit TP, another you go SL to BE. The 2nd lot hit BE, no issue, you still got your 30 pips, right? WRONG!
Borrows exactly what you did: You'd 60 pips in your equity to get both lots, when you transferred SL to BE for 1 lot, it ONLY means you opened a random new trade with -30 SL, when it hits the SL in BE, you lose 30 pips out of YOUR money!!
Two - Moving SL to BE = starting a haphazard trade, a trader who transferred SL to BE within an EU trade is just like a trader who's opening a haphazard order in EU trade with SL = -30 pips.
3-When you start two lots and both hit SL, any new trade BOTH 2 lots must hit TP in order to be profitable, moving SL to BE will decrease your winning % drastically.
4- Have you ever noticed someone goes TP to BE when he is -15 pips?? It makes exactly the identical sense, or possibly a better approach!! Since 1 trade can hit BE and another hit on the -30 pips SL and you shed -30 pips instead of -60!! . So moving SL to BE is only a psychological product where you want to feel safe. While the fact puts you.
5-Why would you move SL to BE? Why not 10 pips or 20 or longer? Because you would like to provide the transaction more room, ideal?? Guess what, keeping the older SL provides the trade MORE room and you have more chance hit your TP!!
6-You are moving out, or going to sleep. . .etc, Then instead of transferring SL to BE, close your 30 pips and input another transaction at a retractment or another pair ! The specific same thing.
Conclusion
Moving SL to BE will reduce your winning percent. If you do your homework and studied confident about% of hitting on TP and your system, never go SL to BE.