Players considered past their best are still important to Arsenal.
When Arsenal signed David Luiz from Chelsea last summer it raised a few eyebrows, he was considered a liability and summed up the Arsenal transfer policy perfectly.
Now, Luiz is a clown, in my opinion, I have made my disdain for him as a footballer very clear on this site from the day he was acquired, however, he does have other uses.
Experience at the highest level is a great asset for any player but it cannot maintain them on the field of play when age catches up with them but it can still be a huge asset off the field.
Of course, you do not sign a player like Luiz to do off field work, that is what coaches are for but you can sign them to play a stop-gap role and help mentor and guide the younger players.
When Arsenal have their backs to the wall it is the job of the senior players to calm the younger players down, to keep them focussed and to mentor them and that applies both on and off the pitch.
I have zero time for Mesut Ozil and feel he should be sold as a matter of urgency, however, only recently Joe Willock revealed the influence that Ozil has on him. The same no doubt applies to the young strikers around Pierre-Emerick Aubameyang (not past his best but still a senior player) or defenders training and playing alongside Luiz.
I would personally like to see David Luiz not to be a starter but someone that can be brought off the bench when the Gunners are trying to see a game out. I would prefer Ozil to be utilised nearer the end of a game when the opposition is tiring, space is being opened up and Arsenal needs a goal. It would also be far better not to see Aubameyang chastising Willock but instead encouraging him.
There is always a role for senior players as long as they are utilised in the right way.