Yes, sometimes you pay backups to sit on the bench.
The obvious situation is QB. We want to have a quality backup. He is really valuable only when there is an injury.
Our offense has a solid set of receivers, and also a fine set of running backs (even with one out).
This season, the offense is not built for a 2 receiving TE's. With Gronk, we have all we need from the TE position, other than occasionally needing a blocking TE in the game.
So, the issue for the GM, as it was last year, was the same. How does one prepare for the possibility that Gronk is out. Who would replace Gronk in the offense that used one TE. That TE needn't have any use whatsoever unless Gronk is injured. If Gronk is injured, the backup needs to be a blocker and pass receiver. However, the more important role is to be a blocker in a one TE set, a blocker who is a potential threat to catch a short pass or a dump off. Ideally, he should be able to be able to catch an intermediate pass.
With Gronk healthy, we don't know whether All can perform the role for which he was signed, a single TE. We guess that since he hasn't done well as a second TE in a 2 TE set, that he is therefore unable to play his primary role, if it ever needed. My bottom line is that if Josh is comfortable that he is OK as a Gronk replacement, Allan can ride the pine.
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So, for me, Allen is an expensive backup for the second most important player on the offense. Sure, we're nervous that Allen won't be ready if he is needed.
That's what he is an expensive backup who was paid to be a bigger part of the offense. I hope you are not the type to say we pay guys to sit on the bench, or be a player coach.