Don't over soften your butter

If your cookies spread too much, it could be that you have let the butter get too soft. Butter should be set out about 30 to 45 minutes before making your cookies, but not longer than that.
The butter should yield  when you gently press on it.

If your butter is too soft when you prepare your cake batter, your cake will be dense. Properly softened butter will give you a tender cake with a delicate crumb.

It is a temptation to microwave butter to make it soft when you're short on time or realized that you forgot to set it out. The results will not be what you want. If you need to soften the butter faster you can cut it into smaller chunks. And then if you want, smash it in your palms to speed the process up.