It's easing, it provides you with time to think and calm your mind- it relieves you from the stress of constantly needing to come up with conversations to talk about when you're with someone, especially after a tiring day where you just don't want to do anything at all. There have been countless times where I will deliberately miss the train/catch it really early just to avoid people (this sounds quite sad I know) but sometimes when things get heavy you'd prefer to enjoy the morning breeze and appreciate the fresh air instead of subjecting yourself to unnecessary conversation which is really a waste of breath when you think about it. 

I think the same applies with shopping- you'd rather go by yourself and shop at your own pace rather than being pressured by your friends to go to shops you don't want to go to, be pressured into buying things you don't need, or even shopping at a faster rate/rush shopping just so you don't inconvenience your friends. And there are times when you think twice and decide that you want to purchase something in a previous store but you can't go back because your friends are with you and they don't want to head back.