This topic come up every so often and I always end up typing until my hands ache. This time, I'll make it short...
Although it is fine for storring wine in the short term (a week or two), you should not make it a habbit to use gas to replace wine in a container.
There are a variety of reasons, but here are the main two..
1) gasses work differently than, say, liquids. You will not be replacing air with gas, but simply mixing air with the gas you are using.
2) if you use a fermentation lock, and there is a large void in your container, temerature and barametric pressure changes will eventually expell the gas you use and take in air through the fermentation lock. Professional wineries do not worry about this because they have their containers under an air-tight pressure seal.
Top off the container with wine or use marbles. There is even one member here that has invented a bladder that can be inserted into a carboy to take up the void. Do not use gas!.