Is it ok to clip component leads after soldering?
I was told to cut the leads to length before soldering. There was an IPC standard around on which basis we were taught that. I don't remember which standard it was exactly.

A reference I found is this document by IPC.


  [...] The next part of the through-hole solder joint is the component lead. [...]  Either way the leads are
  formed – usually with a 90 degree bend – and trimmed to the correct length. After the lead is
  trimmed, it may be clinched or bent over to hold the component in place during the rest of the
  assembly process. [...] The last part of the connection is the solder joint.  [...]


So to prevent parts from falling off, you bent the already trimmed leads over (in a direction where it doesn't cause problems). And after that you solder them.

It is probably taught that way just as @GummiV mentioned in the comment, that the force and shock of the trimming might cause the joint or the PCB to be damaged.

I actually managed to break of a fragile ring with the track once because I was trimming after soldering, so I think the advice of the IPC is quite sound.

There are also frames around which help you in the assembly of through hole boards. You can put the board in, put all your components in from the top, then put down a lid and turn the whole thing around to solder on the bottom side.

Looks something like this: