When it comes to protecting the environment there are some major things we can do to help and there are minor things we can do as well. Yet if everyone does enough of little things to help, then it all adds up to helping the environment.
You should use a reusable grocery bag primarily because it is good for the environment by all means. Reusing a bag means that you do not have to use paper and plastic carrier bags, reducing the over all demand for them. Carrier bags are not good for the environment as they are made of paper and plastic, and often end up in trash cans, or even littering our streets. Over recent years the ecological damage has been reduced a little by using recycled paper and plastic to make carrier bags out of. Still a great deal of damage has already been done due to the sheer number of non-biodegradable plastic bags already buried in landfill sites. The more we use reusable bags, the lower the need for carrier bags.
Using a reusable grocery tote bag fits in with the main ways that we as consumers can limit damage to our environment. It comes under the reuse part of the trilogy of reduce, recycle, and reuse. In fact using your reusable bag helps you to achieve all three. Firstly the majority of reusable bags are partly or wholly made out of recycled materials, secondly you are helping to reduce the number of new disposable bags that are used, thirdly of course you are reusing every time that you use it. Finally many of the reusable bags are completely recyclable so if you can no longer use it just get it recycled so that it's material can be used again.
Another good reason for using a reusable grocery bag is that they are generally stronger than most disposable carrier bags. We all have experienced a plastic carrier splitting before, or a paper one giving way after getting wet in the rain. Fortunately reusable bags are stronger so you are less likely to have to pick up the groceries off the floor.
In some places you have to pay to use disposable carrier bags but not to use reusable ones, so using them saves you money. Also some retailers and supermarkets offer their customers some incentives to reuse bags or use reusable bags by offering loyalty card bonuses or money off from their total shopping bill.