Read Only features are applied to a PART such all the features previous to one feature that has been assigned Read Only will not regenerate. Often people will have a part with repeated geometry (i.e. 300+ general patterned table driven holes) that markedly slows down the performance of a PART. Now when that PART is used in a next assembly, the performance of the assembly slows too. When the features in the PART are reordered such that Read Only features are first and other features that are still deired to be modifiable and later, then using Read Only in the PART allows the part to skip past the features prior to the Read Only, and only regenerate the features in the PART after the Read Only. Sometimes, Pro/E users will simply apply a Read Only feature to the last feature and lock the entire part. That works, but EVERY time you need to modify geometry, you have to Clean the PART model of the Read Only feature. (you might then also re-apply the Read Only feature after finishing the modifications...) It does not affect viewing the model, or even changing parameter strings, or simplified reps, family table instances, etc, but it does allow a part that might take several minutes to regenerate, that is not apt to change, to dramatically improve to only a few seconds regeneration time. Try it.
I would not suggest setting a precedence for saving PARTs with a Read Only feature applied, but for that frustratingly slow component in your bigger assembly(s), going into the slow part and adding the Read Only to the sloth like PART may give you immediate satisfaction. This is an option that may work better than substituting a Simplified Representation of the PART .
I have highlighted PART several times here because the Read Only functionality is ONLY available in Part mode.
