This is a guest post from Sierra Black, a long-time GRS reader and the author of ChildWild, a blog where she writes about frugality, sustainable living, and getting her kids to eat kale. Previously at Get Rich Slowly, Black told us about sweating the big stuff.

Buying in bulk is great, right? You get the things you want and need, and pay less for them. As an added bonus, you don’t have to shop as often (at least, this is a bonus for me, since I hate shopping).

Because I hate shopping and love discounts, I buy most everything in bulk: toilet paper, frozen foods, light bulbs, even toys. But bulk buying has its risks too, and after years of practicing it, I’m learning to see them.

For me, the three key dangers in bulk buying are:

Making a bad investment in a good product that you need or love. I love a particular brand of gel pen, and I use them daily. They cost about $1 per pen in packs of ten, and about $0.50 per pen in packs of 100. I was at the store the other day, trying to decide how many pens to buy. The decision was made for me by the fact that I am on a cash diet at the moment and had only ten dollars in my purse. Yes, I’m paying more per pen. But the 100-pack of pens is an investment. It ties my dollars up in pens, and prevents me from earning interest on them in a savings account.

Here’s a Wall Street Journal article that makes this point about Forever Stamps (which are also a bad investment, but a fine purchase if you use a lot of stamps).

Buying something you might use but don’t need in bulk. My kids love Puffins cereal, so when I got the chance to buy an entire case of it on sale, I did so. This was in January. We just finished the last box of Puffins. Let me tell you, there have been some scenes around the breakfast table in the past six months.

It turns out no one likes Puffins that much. Buying the cereal in bulk might have saved me a few dollars, but it made my kids unhappy about breakfast. That did not improve our quality of life, which is what frugal living is all about for me.

This bulk-buying hazard is the one I fall for most, because I do “save money” doing it. But it creates a sunk cost. I now have 12 boxes of cereal in my cupboard, and I have to eat them or throw away the money I spent. If I’d “saved money” by buying one box and banking the rest of my dollars, I’d have more money available to buy food the kids and I really want to eat, instead of stoically plowing through another box of Puffins.

Buying things you don’t need or want, simply because they are cheap. The other day, I was biking past Harvard when I noticed a book sale going on in the Yard. I happened to have $20 in my pocket, and was strongly tempted to stop and buy $20 worth of books from their table.

Instead, I decided to take my $20 to a bookstore and buy one book from my 30-day list. I got a book I’d been waiting to buy and knew I would read and continue to use for reference, rather than going for the cheaper books I could buy in bulk. I got fewer books, but more value (and less clutter).

Costco, Target and the other big box stores know that people will buy things just because they’re cheap. When you walk into Target the first thing you see is a large section of items for $1. I used to have a habit of tossing $5 – $10 worth of stuff into my cart: novelty socks, pens, candles, stickers.

When I had a buying mindset, all of these things seemed like great deals. I was getting more stuff for less money. Now I try to avoid getting more Stuff, even when it’s cheap. I buy less in bulk — just like I buy less in boutiques — and I’m watching my savings grow because of it.

J.D.’s note: I’m stupid about buying things just because they’re cheap. Or free. I’m always dragging home free Stuff that becomes clutter. Also, Kris just reminded me that I bought a case of my favorite pens last spring. Photo by Listener42.

This article is about Choices, Consumerism, Frugality, Shopping