To answer this question, ask yourself another question. "Do I mind repainting if I don't like the color?" If the answer is "yes", then definitely sample! I pick paint colors for a living and I still sample colors for my own house. Just because you love a color at your friend's house, doesn't mean it will look good in yours. The cost of paint can add up quickly, especially when you have to repaint. The cost of a sample pot and a poster board can save you a lot in the end.
What's the best way to sample?
There are many ways to sample, but in my opinion, only one way is best.
Purchase a large, plastic poster board. I prefer the Mighty Boards that I get at my local Benjamin Moore dealer. (I'm not being compensated for any product placement.)
Purchase a sample pot (1/2 pint or so) and paint 2 coats on the sample board, all the way to the edges.
Roll some tape and put it on the back. Stick the board on a wall, then keep moving it around, in different lighting conditions. The same paint color will look different in each room, and even each wall. Look at your sample during different times of the day, as well as on a sunny day and a grey day.
What NOT to do.
Don't use paper poster boards, as they will absorb the water in the paint and will buckle, distorting how you will see the color. Even rigid foam boards will still warp. You can use a piece of sheet rock, or another smooth surface that will not absorb water.
You can purchase large, stick-on samples from various vendors but I find them too small. Don't go smaller than the Mighty Boards, which are 18" x 24". I visit homes where the homeowner painted a tiny sample on the wall, and in one coat. You just can't tell what it is going to look like by doing that. The more square footage you will be painting, the bigger the sample should be. I've taped two boards together before, which is even better. With every square foot you paint, the undertones in the paint color will pop out even more.
Don't paint your sample right on the wall. If you do, you'll have to sand the edges before painting, otherwise you will see where the sample was. If you plan on having a painter do the job, they will thank you for using a sample board!
Unless your walls are already white, I recommend taping white paper around the sample so it doesn't sit right next to your current wall color. Colors that are right next to each other can play tricks with your mind! In the image above, the colors look different depending on what colors they abut. For a few jobs with very strong existing colors, I've even suggested tacking up a white sheet.
More that a few times, I've changed my mind on a color once I saw it on a larger sample. If you simply can't do a large paint sample, at the very least try to find larger paper samples. Some Benjamin Moore retailers will loan out samples that are up to 8" x 8". They are certainly better than just looking at the tiny swatch on the paint strip. However, I hope you can do the large boards. I hang onto them when I'm done for my next project! Who knows, maybe this will give you the confidence to try something just a bit out of your comfort zone!