You can for sites that can't afford the cost of keeping up-to-date with the Google IP list without which they can lose timely indexing. That is many.
What do you mean by “afford the cost”? The list is free of charge (https://support.google.com/a/answer/10026322?hl=en-GB) and maintenance can be fully automated.
What do you mean by “afford the cost”? The list is free of charge (https://support.google.com/a/answer/10026322?hl=en-GB) and maintenance can be fully automated.