Every time you deliberately touch an item you create a save point. If you later lose track of that item you don't need to go back any further to start looking for it.
I check my phone and wallet before and after I e.g. enter or exit a train. Also if I'm in a dense crowd.
I got pickpocketed only once, 14 years ago, but I have dropped things or randomly left things in places far more often than that.