Personally rus I use 5nm or 1000ft but others ,with just cause use both.
Why?
Busy sequence, lots of stuff going on, vectors on a number of a/c. You have the {insert any airline here as has happened to most} on parallel vectors with slower/faster a/c both on unrestricted decent. Avert your eyes when flight progress strips given to you\checking other a/c on vectors\answering co-ord lines. When you look back you wonder what the
the {insert any airline name here} is doing going direct to a waypoint when should still be on vectors and where the hell your 5nm went. This you get to contemplate during your days off and your retraining for a mistake that someone else caused.
Why retraining? Well 5nm and 1000ft are the
min std. If "deemed" necesary you should use more or multiple std's. Above situation has happened to most of us, the lucky ones were useing a back up std {ie vert} no sep loss, no retraining, just a
up sequence.
Hope this helps understand why we are a bit careful at times.
