Unless you have a fool-proof force, then it's always a good idea to be able to switch to another trick which doesn't require a force. I'd wouldn't use the ID for that though - just a trick which can use any indifferent card to start with. Try the force again later.
In fact it's a good way to practice the force in the first place. Try to force each time you can - it'll get easier each time.
I have in the past carried an ID - but normally only use it when a trick has gone belly up (it does happen...

) and you turn over their card and they say 'Nope. that's not it.'
Even if you know it
was their card, it still happens - people do sometimes mis-remember their card - and the customer is always right after all - a quick change of direction to produce it from the ID works wonders at digging you out of a hole...