Google Analytics Foundation

• Create a copy of your original view instead.
• Views are not retroactive (will not include historical data from other views)

We recommend that you don’t delete or add filters to your original view. When you delete a view, that particular historical perspective of the data is gone. When you add filters to a view, the data you exclude is unavailable. To preserve all your original data and also control the specific perspectives of that data, create a copy of your original view or set up additional views and customize each one to meet your reporting goals.

Learn more about Google Analytics:

1) About Views

https://support.google.com/analytics/answer/2649553?hl=en

2) Three things to remember about Views

https://www.practicalecommerce.com/Google-Analytics-Using-Views-and-Filters-to-Understand-Visitors

• Views are not retroactive
• Always keep the raw data (keep original intact)
• Test before implementing - create a view and test your filters on it to make sure it works.

3) For SaaS projects - exclude dev's from localhost

If you go to:

a) Behavior > Site Content > All Pages 
b) Now apply a secondary dimension of 'Hostname" from Behavior

If you see 'localhost' than your want to remove this data.

https://briefmetrics.com/articles/remove-localhost-from-referrers

c) Create a new filter > exclude > traffic to the hostname > localhost.

NOTE: Filter effects are permanent, meaning once a filter is applied that data is GONE! so make sure not to apply to 'All Website Data' or only apply to it after you have tested it on another.