*pkg removal .. when is it an obligatory step?

[daemonfowl]

Hi everybody !

Can you help me decide what situation(s) a complete removal of packages is a wise and necessary step before an upgrade (current- , i386) ? .. someone -I recall- described such a step as an overkill .. so when is it nothing but an overkill ? and when is it an obligatory step to a clean and stabe system?

( In fact, -laught at it if you feel so- I never did an upgrade without first removing all packages , until yesterday : I upgraded and sysmerged then did a simple pkg_add -u .. it took some time .. it was all ok :-) .. )

Thanks for your help and support!