I think you are misunderstanding the point of the Activity. It will actually not work like how you think. It's only going to add a small delay and if it takes longer than a minute it will go into that sequence of events without care of any other workflow running using the same ID on it's Simple Synchronization Sequence. You will need to be very careful about what you are doing when using this activity.

In terms of the original question, I do not believe that the Retrieve Field Values activity locks the file, so you should not have to worry about that. 

If you are worried about activities failing because of a lock, you might want to introduce a Try-Catch activity and then use it within a Repeat activity and using tokens to control if an activity repeats. This will allow you to catch when an error occurs when you try to access a locked document. 

It likely does not increase any speed but it does allow you to handle the errors you are likely encountering.