One thing being - you have to issue the command for every logical screenyou start. Also, I lost my concatenation when I was in my primary screen - but that could be because it had gone and one of my other screens got left as my only screen and I porbably had not done the ALTLIB. As SYSEXEC is unused (all system stuff goes to SYSPROC) my ALLOC works fine and is issued, in simple terms, to my TSO session and not my ISPF session so it is available to all screens I have active without having to keep track of where I am. Possibly I could use some alternative form of ALTLIB to get around the problem but - why should I?
The problem I have is that people can explain things quickly but I can only comprehend slowly.