Lets talk Emotional decluttering.
This can prevent the best willed people from separating themselves from belongings they have had for decades, with the knowledge it will honestly never be looked at again.
There are many reasons why this happens. Children that that flown the nest, leaving parents, mothers primarily with the 'empty syndrome', close relatives that have pasted away and even may have left their full estate to someone to sort out.
It is important to say that emotional clears can take longer and you are right not to rush the process, this can lead to regret later down the line. If something is not ready to be parted with, it can still be organised and clearly labelled for future decluttering, which will be time saving.
It is also important to start feeling your emotions and attachments to things, for example: strong must keeps, make you remember positive memories, feel positive, happy.
Remember that there are other ways to remember then just by keeping an object, like having a picture, which is smaller and a memory trigger or knowing that you ill see this item around else where, which will also trigger memories.
Creating a memory box for a person who has died is also a nice idea, then keeping a wardrobe they once owned which has not significate emotional attachment other then it was owned by the person you are missing.
It is worth the storage space if its going to play on your mind, return to it later, but do return to it. you will subconsciously play around with it in your mind over the next day or two.