Assistants to Managers - does it work?

Based on an article I read this morning on the BBC site regarding Kevin Keen wanting the job at West Ham full time, I am wondering whether this is a good move.

For some reason it seems to be a real trend to sack the manager and allow the assistant to take charge, initially temporarily, but often full time. Is this ever a good idea? I mean if the manager has had to be sacked for performance, then surely his assistant must have been underperforming too?

Then there is the aspect of the assistant being closer to the players than the manager, and in a lot of cases, more like a friend. Can this transition so easily to being the 'boss'?

Thinking of recent examples where it has worked, see Hughton at Newcastle, but then where it seems to be failing, see Steve Kean at Blackburn.

I'm sure there are plenty of cases of it working and not working, so if you can think of any please list them. But do you think it works?

I think it depends if they are assistant manager, or assistant to the manager.

For instance, I think someone like Malky Mackay at Watford works well because he genuinely assisted Brendan Rogers and contributed as well as learned.

Whearas Steve Kean probably just got Big Sam his coffee, hid his wads of cash around where the FA couldn't find them, and booked his annual trip to see Celine Dion.

It can work, in my view it's currently working well at Carlisle United Abbott is doing a good job after being the Assistant Manager for a few seasons under different managers. He's completely changed the squad from when Ward was here, we play different formations, we play a different style of football. Also you can use the caretaker manager period to see if they do have different ideas to the man you've just sacked or if they're exactly the same.

Im not sure if assistant managers should be promoted if the manager gets sacked. If you look at Fergusons assistants at Man Utd none of them have left and achieved much success on their own namely Quieroz and McClaren. Steve Clarke did well at Chelsea, West Ham and now Liverpool but he is seen more as a first team coach rather than an assistant manager.