In most cases, your own institution will not bag you, you are representing them on the interviews and applications.
But, in general, I believe it is frowned upon to not waive your right - it implies that you pre-screened your evals to make sure there was nothing derogatory and it poses an uncomfortable atmosphere between you and your evaluator. i.e. the eval may not be totally "honest" with them knowing you are going to read it.
Just make sure you know your evaluator well and speak frankly with them prior to having them write you an eval - if you are close, they will often show it to you despite your waiving the right.