Thanks for explanation. But can I transfer that change from change address back to my lets call it "primary" address that I use to keep most of my BTCs?
I lack reputation to answer to your second question, so I will answer here.
There is a very good reason to consolidate all your balance into one, if you are not worried about privacy: To save on fees.
You have a lot of addresses, all of them have balances, and you have a lot of change addresses. Every time you make a transaction you will consume the balance of those addresses as an extra input, which will increase transaction size and fees.
Now, as the network is really congested, you shouldn't consolidate your balance in one address. But in a few weeks the fees will be low again. Simple make a transaction of your entire balance to an address of your wallet (it can be a new or old one). As you are transferring for yourself, you can use a 1 sat/byte fee and wait for as long as necessary.
When you consolidate balance you will save in fees your next transactions (as you will have fewer inputs).